Source code for sympy.printing.fcode

"""
Fortran code printer

The FCodePrinter converts single sympy expressions into single Fortran
expressions, using the functions defined in the Fortran 77 standard where
possible. Some useful pointers to Fortran can be found on wikipedia:

http://en.wikipedia.org/wiki/Fortran

Most of the code below is based on the "Professional Programmer\'s Guide to
Fortran77" by Clive G. Page:

http://www.star.le.ac.uk/~cgp/prof77.html

Fortran is a case-insensitive language. This might cause trouble because
SymPy is case sensitive. So, fcode adds underscores to variable names when
it is necessary to make them different for Fortran.
"""

from __future__ import print_function, division

from collections import defaultdict
from itertools import chain
import string

from sympy.core import S, Add, N, Float, Symbol
from sympy.core.compatibility import string_types, range
from sympy.core.function import Function
from sympy.core.relational import Eq
from sympy.sets import Range
from sympy.codegen.ast import (
    Assignment, Attribute, Declaration, Pointer, Type, value_const,
    float32, float64, float80, complex64, complex128, int8, int16, int32,
    int64, intc, real, integer,  bool_, complex_
)
from sympy.codegen.fnodes import (
    allocatable, isign, dsign, cmplx, merge, literal_dp, elemental, pure,
    intent_in, intent_out, intent_inout
)
from sympy.printing.printer import printer_context
from sympy.printing.codeprinter import CodePrinter, requires
from sympy.printing.precedence import precedence, PRECEDENCE


known_functions = {
    "sin": "sin",
    "cos": "cos",
    "tan": "tan",
    "asin": "asin",
    "acos": "acos",
    "atan": "atan",
    "atan2": "atan2",
    "sinh": "sinh",
    "cosh": "cosh",
    "tanh": "tanh",
    "log": "log",
    "exp": "exp",
    "erf": "erf",
    "Abs": "abs",
    "conjugate": "conjg",
    "Max": "max",
    "Min": "min",
}


[docs]class FCodePrinter(CodePrinter): """A printer to convert sympy expressions to strings of Fortran code""" printmethod = "_fcode" language = "Fortran" type_aliases = { integer: int32, real: float64, complex_: complex128, } type_mappings = { intc: 'integer(c_int)', float32: 'real*4', # real(kind(0.e0)) float64: 'real*8', # real(kind(0.d0)) float80: 'real*10', # real(kind(????)) complex64: 'complex*8', complex128: 'complex*16', int8: 'integer*1', int16: 'integer*2', int32: 'integer*4', int64: 'integer*8', bool_: 'logical' } type_modules = { intc: {'iso_c_binding': 'c_int'} } _default_settings = { 'order': None, 'full_prec': 'auto', 'precision': 17, 'user_functions': {}, 'human': True, 'allow_unknown_functions': False, 'source_format': 'fixed', 'contract': True, 'standard': 77, 'name_mangling' : True, } _operators = { 'and': '.and.', 'or': '.or.', 'xor': '.neqv.', 'equivalent': '.eqv.', 'not': '.not. ', } _relationals = { '!=': '/=', } def __init__(self, settings={}): self.mangled_symbols = {} ## Dict showing mapping of all words self.used_name= [] self.type_aliases = dict(chain(self.type_aliases.items(), settings.pop('type_aliases', {}).items())) self.type_mappings = dict(chain(self.type_mappings.items(), settings.pop('type_mappings', {}).items())) super(FCodePrinter, self).__init__(settings) self.known_functions = dict(known_functions) userfuncs = settings.get('user_functions', {}) self.known_functions.update(userfuncs) # leading columns depend on fixed or free format standards = {66, 77, 90, 95, 2003, 2008} if self._settings['standard'] not in standards: raise ValueError("Unknown Fortran standard: %s" % self._settings[ 'standard']) self.module_uses = defaultdict(set) # e.g.: use iso_c_binding, only: c_int @property def _lead(self): if self._settings['source_format'] == 'fixed': return {'code': " ", 'cont': " @ ", 'comment': "C "} elif self._settings['source_format'] == 'free': return {'code': "", 'cont': " ", 'comment': "! "} else: raise ValueError("Unknown source format: %s" % self._settings['source_format']) def _print_Symbol(self, expr): if self._settings['name_mangling'] == True: if expr not in self.mangled_symbols: name = expr.name while name.lower() in self.used_name: name += '_' self.used_name.append(name.lower()) if name == expr.name: self.mangled_symbols[expr] = expr else: self.mangled_symbols[expr] = Symbol(name) expr = expr.xreplace(self.mangled_symbols) name = super(FCodePrinter, self)._print_Symbol(expr) return name def _rate_index_position(self, p): return -p*5 def _get_statement(self, codestring): return codestring def _get_comment(self, text): return "! {0}".format(text) def _declare_number_const(self, name, value): return "parameter ({0} = {1})".format(name, self._print(value)) def _print_NumberSymbol(self, expr): # A Number symbol that is not implemented here or with _printmethod # is registered and evaluated self._number_symbols.add((expr, Float(expr.evalf(self._settings['precision'])))) return str(expr) def _format_code(self, lines): return self._wrap_fortran(self.indent_code(lines)) def _traverse_matrix_indices(self, mat): rows, cols = mat.shape return ((i, j) for j in range(cols) for i in range(rows)) def _get_loop_opening_ending(self, indices): open_lines = [] close_lines = [] for i in indices: # fortran arrays start at 1 and end at dimension var, start, stop = map(self._print, [i.label, i.lower + 1, i.upper + 1]) open_lines.append("do %s = %s, %s" % (var, start, stop)) close_lines.append("end do") return open_lines, close_lines def _print_sign(self, expr): from sympy import Abs arg, = expr.args if arg.is_integer: new_expr = merge(0, isign(1, arg), Eq(arg, 0)) elif arg.is_complex: new_expr = merge(cmplx(literal_dp(0), literal_dp(0)), arg/Abs(arg), Eq(Abs(arg), literal_dp(0))) else: new_expr = merge(literal_dp(0), dsign(literal_dp(1), arg), Eq(arg, literal_dp(0))) return self._print(new_expr) def _print_Piecewise(self, expr): if expr.args[-1].cond != True: # We need the last conditional to be a True, otherwise the resulting # function may not return a result. raise ValueError("All Piecewise expressions must contain an " "(expr, True) statement to be used as a default " "condition. Without one, the generated " "expression may not evaluate to anything under " "some condition.") lines = [] if expr.has(Assignment): for i, (e, c) in enumerate(expr.args): if i == 0: lines.append("if (%s) then" % self._print(c)) elif i == len(expr.args) - 1 and c == True: lines.append("else") else: lines.append("else if (%s) then" % self._print(c)) lines.append(self._print(e)) lines.append("end if") return "\n".join(lines) elif self._settings["standard"] >= 95: # Only supported in F95 and newer: # The piecewise was used in an expression, need to do inline # operators. This has the downside that inline operators will # not work for statements that span multiple lines (Matrix or # Indexed expressions). pattern = "merge({T}, {F}, {COND})" code = self._print(expr.args[-1].expr) terms = list(expr.args[:-1]) while terms: e, c = terms.pop() expr = self._print(e) cond = self._print(c) code = pattern.format(T=expr, F=code, COND=cond) return code else: # `merge` is not supported prior to F95 raise NotImplementedError("Using Piecewise as an expression using " "inline operators is not supported in " "standards earlier than Fortran95.") def _print_MatrixElement(self, expr): return "{0}({1}, {2})".format(self.parenthesize(expr.parent, PRECEDENCE["Atom"], strict=True), expr.i + 1, expr.j + 1) def _print_Add(self, expr): # purpose: print complex numbers nicely in Fortran. # collect the purely real and purely imaginary parts: pure_real = [] pure_imaginary = [] mixed = [] for arg in expr.args: if arg.is_number and arg.is_real: pure_real.append(arg) elif arg.is_number and arg.is_imaginary: pure_imaginary.append(arg) else: mixed.append(arg) if len(pure_imaginary) > 0: if len(mixed) > 0: PREC = precedence(expr) term = Add(*mixed) t = self._print(term) if t.startswith('-'): sign = "-" t = t[1:] else: sign = "+" if precedence(term) < PREC: t = "(%s)" % t return "cmplx(%s,%s) %s %s" % ( self._print(Add(*pure_real)), self._print(-S.ImaginaryUnit*Add(*pure_imaginary)), sign, t, ) else: return "cmplx(%s,%s)" % ( self._print(Add(*pure_real)), self._print(-S.ImaginaryUnit*Add(*pure_imaginary)), ) else: return CodePrinter._print_Add(self, expr) def _print_Function(self, expr): # All constant function args are evaluated as floats prec = self._settings['precision'] args = [N(a, prec) for a in expr.args] eval_expr = expr.func(*args) if not isinstance(eval_expr, Function): return self._print(eval_expr) else: return CodePrinter._print_Function(self, expr.func(*args)) def _print_Mod(self, expr): # NOTE : Fortran has the functions mod() and modulo(). modulo() behaves # the same wrt to the sign of the arguments as Python and SymPy's # modulus computations (% and Mod()) but is not available in Fortran 66 # or Fortran 77, thus we raise an error. if self._settings['standard'] in [66, 77]: msg = ("Python % operator and SymPy's Mod() function are not " "supported by Fortran 66 or 77 standards.") raise NotImplementedError(msg) else: x, y = expr.args return " modulo({}, {})".format(self._print(x), self._print(y)) def _print_ImaginaryUnit(self, expr): # purpose: print complex numbers nicely in Fortran. return "cmplx(0,1)" def _print_int(self, expr): return str(expr) def _print_Mul(self, expr): # purpose: print complex numbers nicely in Fortran. if expr.is_number and expr.is_imaginary: return "cmplx(0,%s)" % ( self._print(-S.ImaginaryUnit*expr) ) else: return CodePrinter._print_Mul(self, expr) def _print_Pow(self, expr): PREC = precedence(expr) if expr.exp == -1: return '%s/%s' % ( self._print(literal_dp(1)), self.parenthesize(expr.base, PREC) ) elif expr.exp == 0.5: if expr.base.is_integer: # Fortran intrinsic sqrt() does not accept integer argument if expr.base.is_Number: return 'sqrt(%s.0d0)' % self._print(expr.base) else: return 'sqrt(dble(%s))' % self._print(expr.base) else: return 'sqrt(%s)' % self._print(expr.base) else: return CodePrinter._print_Pow(self, expr) def _print_Rational(self, expr): p, q = int(expr.p), int(expr.q) return "%d.0d0/%d.0d0" % (p, q) def _print_Float(self, expr): printed = CodePrinter._print_Float(self, expr) e = printed.find('e') if e > -1: return "%sd%s" % (printed[:e], printed[e + 1:]) return "%sd0" % printed def _print_Indexed(self, expr): inds = [ self._print(i) for i in expr.indices ] return "%s(%s)" % (self._print(expr.base.label), ", ".join(inds)) def _print_Idx(self, expr): return self._print(expr.label) def _print_AugmentedAssignment(self, expr): lhs_code = self._print(expr.lhs) rhs_code = self._print(expr.rhs) return self._get_statement("{0} = {0} {1} {2}".format( *map(lambda arg: self._print(arg), [lhs_code, expr.binop, rhs_code]))) def _print_sum_(self, sm): params = self._print(sm.array) if sm.dim != None: params += ', ' + self._print(sm.dim) if sm.mask != None: params += ', mask=' + self._print(sm.mask) return '%s(%s)' % (sm.__class__.__name__.rstrip('_'), params) def _print_product_(self, prod): return self._print_sum_(prod) def _print_Do(self, do): excl = ['concurrent'] if do.step == 1: excl.append('step') step = '' else: step = ', {step}' return ( 'do {concurrent}{counter} = {first}, {last}'+step+'\n' '{body}\n' 'end do\n' ).format( concurrent='concurrent ' if do.concurrent else '', **do.kwargs(apply=lambda arg: self._print(arg), exclude=excl) ) def _print_ImpliedDoLoop(self, idl): step = '' if idl.step == 1 else ', {step}' return ('({expr}, {counter} = {first}, {last}'+step+')').format( **idl.kwargs(apply=lambda arg: self._print(arg)) ) def _print_For(self, expr): target = self._print(expr.target) if isinstance(expr.iterable, Range): start, stop, step = expr.iterable.args else: raise NotImplementedError("Only iterable currently supported is Range") body = self._print(expr.body) return ('do {target} = {start}, {stop}, {step}\n' '{body}\n' 'end do').format(target=target, start=start, stop=stop, step=step, body=body) def _print_Equality(self, expr): lhs, rhs = expr.args return ' == '.join(map(lambda arg: self._print(arg), (lhs, rhs))) def _print_Unequality(self, expr): lhs, rhs = expr.args return ' /= '.join(map(lambda arg: self._print(arg), (lhs, rhs))) def _print_Type(self, type_): type_ = self.type_aliases.get(type_, type_) type_str = self.type_mappings.get(type_, type_.name) module_uses = self.type_modules.get(type_) if module_uses: for k, v in module_uses: self.module_uses[k].add(v) return type_str def _print_Element(self, elem): return '{symbol}({idxs})'.format( symbol=self._print(elem.symbol), idxs=', '.join(map(lambda arg: self._print(arg), elem.indices)) ) def _print_Extent(self, ext): return str(ext) def _print_Declaration(self, expr): var = expr.variable val = var.value dim = var.attr_params('dimension') intents = [intent in var.attrs for intent in (intent_in, intent_out, intent_inout)] if intents.count(True) == 0: intent = '' elif intents.count(True) == 1: intent = ', intent(%s)' % ['in', 'out', 'inout'][intents.index(True)] else: raise ValueError("Multiple intents specified for %s" % self) if isinstance(var, Pointer): raise NotImplementedError("Pointers are not available by default in Fortran.") if self._settings["standard"] >= 90: result = '{t}{vc}{dim}{intent}{alloc} :: {s}'.format( t=self._print(var.type), vc=', parameter' if value_const in var.attrs else '', dim=', dimension(%s)' % ', '.join(map(lambda arg: self._print(arg), dim)) if dim else '', intent=intent, alloc=', allocatable' if allocatable in var.attrs else '', s=self._print(var.symbol) ) if val != None: result += ' = %s' % self._print(val) else: if value_const in var.attrs or val: raise NotImplementedError("F77 init./parameter statem. req. multiple lines.") result = ' '.join(map(lambda arg: self._print(arg), [var.type, var.symbol])) return result def _print_Infinity(self, expr): return '(huge(%s) + 1)' % self._print(literal_dp(0)) def _print_While(self, expr): return 'do while ({condition})\n{body}\nend do'.format(**expr.kwargs( apply=lambda arg: self._print(arg))) def _print_BooleanTrue(self, expr): return '.true.' def _print_BooleanFalse(self, expr): return '.false.' def _pad_leading_columns(self, lines): result = [] for line in lines: if line.startswith('!'): result.append(self._lead['comment'] + line[1:].lstrip()) else: result.append(self._lead['code'] + line) return result def _wrap_fortran(self, lines): """Wrap long Fortran lines Argument: lines -- a list of lines (without \\n character) A comment line is split at white space. Code lines are split with a more complex rule to give nice results. """ # routine to find split point in a code line my_alnum = set("_+-." + string.digits + string.ascii_letters) my_white = set(" \t()") def split_pos_code(line, endpos): if len(line) <= endpos: return len(line) pos = endpos split = lambda pos: \ (line[pos] in my_alnum and line[pos - 1] not in my_alnum) or \ (line[pos] not in my_alnum and line[pos - 1] in my_alnum) or \ (line[pos] in my_white and line[pos - 1] not in my_white) or \ (line[pos] not in my_white and line[pos - 1] in my_white) while not split(pos): pos -= 1 if pos == 0: return endpos return pos # split line by line and add the split lines to result result = [] if self._settings['source_format'] == 'free': trailing = ' &' else: trailing = '' for line in lines: if line.startswith(self._lead['comment']): # comment line if len(line) > 72: pos = line.rfind(" ", 6, 72) if pos == -1: pos = 72 hunk = line[:pos] line = line[pos:].lstrip() result.append(hunk) while len(line) > 0: pos = line.rfind(" ", 0, 66) if pos == -1 or len(line) < 66: pos = 66 hunk = line[:pos] line = line[pos:].lstrip() result.append("%s%s" % (self._lead['comment'], hunk)) else: result.append(line) elif line.startswith(self._lead['code']): # code line pos = split_pos_code(line, 72) hunk = line[:pos].rstrip() line = line[pos:].lstrip() if line: hunk += trailing result.append(hunk) while len(line) > 0: pos = split_pos_code(line, 65) hunk = line[:pos].rstrip() line = line[pos:].lstrip() if line: hunk += trailing result.append("%s%s" % (self._lead['cont'], hunk)) else: result.append(line) return result
[docs] def indent_code(self, code): """Accepts a string of code or a list of code lines""" if isinstance(code, string_types): code_lines = self.indent_code(code.splitlines(True)) return ''.join(code_lines) free = self._settings['source_format'] == 'free' code = [ line.lstrip(' \t') for line in code ] inc_keyword = ('do ', 'if(', 'if ', 'do\n', 'else', 'program', 'interface') dec_keyword = ('end do', 'enddo', 'end if', 'endif', 'else', 'end program', 'end interface') increase = [ int(any(map(line.startswith, inc_keyword))) for line in code ] decrease = [ int(any(map(line.startswith, dec_keyword))) for line in code ] continuation = [ int(any(map(line.endswith, ['&', '&\n']))) for line in code ] level = 0 cont_padding = 0 tabwidth = 3 new_code = [] for i, line in enumerate(code): if line == '' or line == '\n': new_code.append(line) continue level -= decrease[i] if free: padding = " "*(level*tabwidth + cont_padding) else: padding = " "*level*tabwidth line = "%s%s" % (padding, line) if not free: line = self._pad_leading_columns([line])[0] new_code.append(line) if continuation[i]: cont_padding = 2*tabwidth else: cont_padding = 0 level += increase[i] if not free: return self._wrap_fortran(new_code) return new_code
def _print_GoTo(self, goto): if goto.expr: # computed goto return "go to ({labels}), {expr}".format( labels=', '.join(map(lambda arg: self._print(arg), goto.labels)), expr=self._print(goto.expr) ) else: lbl, = goto.labels return "go to %s" % self._print(lbl) def _print_Program(self, prog): return ( "program {name}\n" "{body}\n" "end program\n" ).format(**prog.kwargs(apply=lambda arg: self._print(arg))) def _print_Module(self, mod): return ( "module {name}\n" "{declarations}\n" "\ncontains\n\n" "{definitions}\n" "end module\n" ).format(**mod.kwargs(apply=lambda arg: self._print(arg))) def _print_Stream(self, strm): if strm.name == 'stdout' and self._settings["standard"] >= 2003: self.module_uses['iso_c_binding'].add('stdint=>input_unit') return 'input_unit' elif strm.name == 'stderr' and self._settings["standard"] >= 2003: self.module_uses['iso_c_binding'].add('stdint=>error_unit') return 'error_unit' else: if strm.name == 'stdout': return '*' else: return strm.name def _print_Print(self, ps): if ps.format_string != None: fmt = self._print(ps.format_string) else: fmt = "*" return "print {fmt}, {iolist}".format(fmt=fmt, iolist=', '.join( map(lambda arg: self._print(arg), ps.print_args))) def _print_Return(self, rs): arg, = rs.args return "{result_name} = {arg}".format( result_name=self._context.get('result_name', 'sympy_result'), arg=self._print(arg) ) def _print_FortranReturn(self, frs): arg, = frs.args if arg: return 'return %s' % self._print(arg) else: return 'return' def _head(self, entity, fp, **kwargs): bind_C_params = fp.attr_params('bind_C') if bind_C_params is None: bind = '' else: bind = ' bind(C, name="%s")' % bind_C_params[0] if bind_C_params else ' bind(C)' result_name = self._settings.get('result_name', None) return ( "{entity}{name}({arg_names}){result}{bind}\n" "{arg_declarations}" ).format( entity=entity, name=self._print(fp.name), arg_names=', '.join([self._print(arg.symbol) for arg in fp.parameters]), result=(' result(%s)' % result_name) if result_name else '', bind=bind, arg_declarations='\n'.join(map(lambda arg: self._print(Declaration(arg)), fp.parameters)) ) def _print_FunctionPrototype(self, fp): entity = "{0} function ".format(self._print(fp.return_type)) return ( "interface\n" "{function_head}\n" "end function\n" "end interface" ).format(function_head=self._head(entity, fp, *args)) def _print_FunctionDefinition(self, fd): if elemental in fd.attrs: prefix = 'elemental ' elif pure in fd.attrs: prefix = 'pure ' else: prefix = '' entity = "{0} function ".format(self._print(fd.return_type)) with printer_context(self, result_name=fd.name): return ( "{prefix}{function_head}\n" "{body}\n" "end function\n" ).format( prefix=prefix, function_head=self._head(entity, fd), body=self._print(fd.body) ) def _print_Subroutine(self, sub): return ( '{subroutine_head}\n' '{body}\n' 'end subroutine\n' ).format( subroutine_head=self._head('subroutine ', sub), body=self._print(sub.body) ) def _print_SubroutineCall(self, scall): return 'call {name}({args})'.format( name=self._print(scall.name), args=', '.join(map(lambda arg: self._print(arg), scall.subroutine_args)) ) def _print_use_rename(self, rnm): return "%s => %s" % tuple(map(lambda arg: self._print(arg), rnm.args)) def _print_use(self, use): result = 'use %s' % self._print(use.namespace) if use.rename != None: result += ', ' + ', '.join([self._print(rnm) for rnm in use.rename]) if use.only != None: result += ', only: ' + ', '.join([self._print(nly) for nly in use.only]) return result def _print_BreakToken(self, _): return 'exit' def _print_ContinueToken(self, _): return 'cycle' def _print_ArrayConstructor(self, ac): fmtstr = "[%s]" if self._settings["standard"] >= 2003 else '(/%s/)' return fmtstr % ', '.join(map(lambda arg: self._print(arg), ac.elements))
[docs]def fcode(expr, assign_to=None, **settings): """Converts an expr to a string of fortran code Parameters ========== expr : Expr A sympy expression to be converted. assign_to : optional When given, the argument is used as the name of the variable to which the expression is assigned. Can be a string, ``Symbol``, ``MatrixSymbol``, or ``Indexed`` type. This is helpful in case of line-wrapping, or for expressions that generate multi-line statements. precision : integer, optional DEPRECATED. Use type_mappings instead. The precision for numbers such as pi [default=17]. user_functions : dict, optional A dictionary where keys are ``FunctionClass`` instances and values are their string representations. Alternatively, the dictionary value can be a list of tuples i.e. [(argument_test, cfunction_string)]. See below for examples. human : bool, optional If True, the result is a single string that may contain some constant declarations for the number symbols. If False, the same information is returned in a tuple of (symbols_to_declare, not_supported_functions, code_text). [default=True]. contract: bool, optional If True, ``Indexed`` instances are assumed to obey tensor contraction rules and the corresponding nested loops over indices are generated. Setting contract=False will not generate loops, instead the user is responsible to provide values for the indices in the code. [default=True]. source_format : optional The source format can be either 'fixed' or 'free'. [default='fixed'] standard : integer, optional The Fortran standard to be followed. This is specified as an integer. Acceptable standards are 66, 77, 90, 95, 2003, and 2008. Default is 77. Note that currently the only distinction internally is between standards before 95, and those 95 and after. This may change later as more features are added. name_mangling : bool, optional If True, then the variables that would become identical in case-insensitive Fortran are mangled by appending different number of ``_`` at the end. If False, SymPy won't interfere with naming of variables. [default=True] Examples ======== >>> from sympy import fcode, symbols, Rational, sin, ceiling, floor >>> x, tau = symbols("x, tau") >>> fcode((2*tau)**Rational(7, 2)) ' 8*sqrt(2.0d0)*tau**(7.0d0/2.0d0)' >>> fcode(sin(x), assign_to="s") ' s = sin(x)' Custom printing can be defined for certain types by passing a dictionary of "type" : "function" to the ``user_functions`` kwarg. Alternatively, the dictionary value can be a list of tuples i.e. [(argument_test, cfunction_string)]. >>> custom_functions = { ... "ceiling": "CEIL", ... "floor": [(lambda x: not x.is_integer, "FLOOR1"), ... (lambda x: x.is_integer, "FLOOR2")] ... } >>> fcode(floor(x) + ceiling(x), user_functions=custom_functions) ' CEIL(x) + FLOOR1(x)' ``Piecewise`` expressions are converted into conditionals. If an ``assign_to`` variable is provided an if statement is created, otherwise the ternary operator is used. Note that if the ``Piecewise`` lacks a default term, represented by ``(expr, True)`` then an error will be thrown. This is to prevent generating an expression that may not evaluate to anything. >>> from sympy import Piecewise >>> expr = Piecewise((x + 1, x > 0), (x, True)) >>> print(fcode(expr, tau)) if (x > 0) then tau = x + 1 else tau = x end if Support for loops is provided through ``Indexed`` types. With ``contract=True`` these expressions will be turned into loops, whereas ``contract=False`` will just print the assignment expression that should be looped over: >>> from sympy import Eq, IndexedBase, Idx >>> len_y = 5 >>> y = IndexedBase('y', shape=(len_y,)) >>> t = IndexedBase('t', shape=(len_y,)) >>> Dy = IndexedBase('Dy', shape=(len_y-1,)) >>> i = Idx('i', len_y-1) >>> e=Eq(Dy[i], (y[i+1]-y[i])/(t[i+1]-t[i])) >>> fcode(e.rhs, assign_to=e.lhs, contract=False) ' Dy(i) = (y(i + 1) - y(i))/(t(i + 1) - t(i))' Matrices are also supported, but a ``MatrixSymbol`` of the same dimensions must be provided to ``assign_to``. Note that any expression that can be generated normally can also exist inside a Matrix: >>> from sympy import Matrix, MatrixSymbol >>> mat = Matrix([x**2, Piecewise((x + 1, x > 0), (x, True)), sin(x)]) >>> A = MatrixSymbol('A', 3, 1) >>> print(fcode(mat, A)) A(1, 1) = x**2 if (x > 0) then A(2, 1) = x + 1 else A(2, 1) = x end if A(3, 1) = sin(x) """ return FCodePrinter(settings).doprint(expr, assign_to)