Bug in ODE solving?

asked 2018-08-30 04:31:21 +0100

Chernoxyl
31 ●2 ●2 ●7

updated 2023-01-09 23:59:47 +0100

tmonteil
27423 ●31 ●204 ●517 http://wiki.sagemath.o...

I am trying to solve this equation system

F’(x) = Sin(x)*F(x)+G(x) G’(x) = F(x)

For some reason, putting this in sagemath:

var('xx','real')
assume(xx>0)
assume(sin(xx)>0)
f,g=[function(i)(xx) for i in 'fg']
eq= [g+sin(xx)*f==diff(f),diff(g)-f==0]
desolve_system(eq,[f,g],ivar=xx)

It yield an error:

 ---------------------------------------------------------------------------

ValueError Traceback (most recent call last) <ipython-input-1-71dd73b24497> in <module>() 4 f,g=[function(i)(xx) for i in 'fg'] 5 eq= [g+sin(xx)*f==diff(f),diff(g)-f==Integer(0)] ----> 6 desolve_system(eq,[f,g],ivar=xx)

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/calculus/desolvers.pyc in desolve_system(des, vars, ics, ivar) 838 soln = list(soln) 839 for i, sol in enumerate(soln): --> 840 soln[i] = sol.sage() 841 if ics is not None: 842 ivar_ic = ics[0]

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/interfaces/interface.pyc in sage(self, args, *kwds) 1049 [0 0] 1050 """ -> 1051 return self._sage_(args, *kwds) 1052 1053 def __repr__(self):

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/interfaces/maxima_abstract.pyc in _sage_(self) 1236 import sage.calculus.calculus as calculus 1237 return calculus.symbolic_expression_from_maxima_string(self.name(), -> 1238 maxima=self.parent()) 1239 1240 def _symbolic_(self, R):

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/calculus/calculus.pyc in symbolic_expression_from_maxima_string(x, equals_sub, maxima) 2153 global _augmented_syms 2154 _augmented_syms = syms -> 2155 return SRM_parser.parse_sequence(s) 2156 finally: 2157 _augmented_syms = {}

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.parse_sequence (build/cythonized/sage/misc/parser.c:5409)() 537 return expr 538 --> 539 cpdef parse_sequence(self, s): 540 """ 541 Parse a (possibly nested) set of lists and tuples.

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.parse_sequence (build/cythonized/sage/misc/parser.c:5276)() 553 """ 554 cdef Tokenizer tokens = Tokenizer(s) --> 555 all = self.p_sequence(tokens) 556 if tokens.next() != EOS: 557 self.parse_error(tokens)

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_sequence (build/cythonized/sage/misc/parser.c:6213)() 626 return all 627 else: --> 628 obj = self.p_eqn(tokens) 629 PyList_Append(all, obj) 630 token = tokens.next()

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_eqn (build/cythonized/sage/misc/parser.c:7123)() 719 cdef int op = tokens.next() 720 if op == '=': --> 721 return lhs == self.p_expr(tokens) 722 elif op == NOT_EQ: 723 return lhs != self.p_expr(tokens)

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_expr (build/cythonized/sage/misc/parser.c:7489)() 756 # Note: this is left-recursive, so we can't just recurse 757 cdef int op --> 758 operand1 = self.p_term(tokens) 759 op = tokens.next() 760 while op == '+' or op == '-':

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_term (build/cythonized/sage/misc/parser.c:7769)() 790 # Note: this is left-recursive, so we can't just recurse 791 cdef int op --> 792 operand1 = self.p_factor(tokens) 793 op = tokens.next() 794 if op == NAME and self.implicit_multiplication:

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_factor (build/cythonized/sage/misc/parser.c:8224)() 833 else: 834 tokens.backtrack() --> 835 return self.p_power(tokens) 836 837 # power ::= (atom | atom!) ^ factor | atom | atom!

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_power (build/cythonized/sage/misc/parser.c:8387)() 861 862 """ --> 863 operand1 = self.p_atom(tokens) 864 cdef int token = tokens.next() 865 if token == '^':

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_atom (build/cythonized/sage/misc/parser.c:9056)() 916 if token == '(': 917 func = self.callable_constructor(name) --> 918 args, kwds = self.p_args(tokens) 919 token = tokens.next() 920 if token != ')':

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_args (build/cythonized/sage/misc/parser.c:9611)() 953 cdef int token = ',' 954 while token == ',': --> 955 arg = self.p_arg(tokens) 956 if isinstance(arg, tuple): 957 name, value = arg

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_arg (build/cythonized/sage/misc/parser.c:10044)() 1003 else: 1004 tokens.backtrack() -> 1005 return self.p_expr(tokens) 1006 1007 cdef parse_error(self, Tokenizer tokens, msg="Malformed expression"):

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_atom (build/cythonized/sage/misc/parser.c:9280)() 925 return self.variable_constructor(name) 926 elif token == '(': --> 927 expr = self.p_expr(tokens) 928 token = tokens.next() 929 if token != ')':

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_term (build/cythonized/sage/misc/parser.c:7854)() 796 tokens.backtrack() 797 while op == '' or op == '/': --> 798 operand2 = self.p_factor(tokens) 799 if op == '': 800 operand1 = operand1 * operand2

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/misc/parser.pyx in sage.misc.parser.Parser.p_atom (build/cythonized/sage/misc/parser.c:9171)() 920 if token != ')': 921 self.parse_error(tokens, "Bad function call") --> 922 return func(args, *kwds) 923 else: 924 tokens.backtrack()

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/calculus/calculus.pyc in dummy_laplace(args) 1871 laplace(f(t), t, s) 1872 """ -> 1873 return _laplace(args[0], var(repr(args[1])), var(repr(args[2]))) 1874 1875 def dummy_inverse_laplace(args):

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/symbolic/ring.pyx in sage.symbolic.ring.var (build/cythonized/sage/symbolic/ring.cpp:14039)() 1297 ValueError: The name "3" is not a valid Python identifier. 1298 """ -> 1299 return SR.var(name, **kwds) 1300 1301 def is_SymbolicVariable(x):

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/symbolic/ring.pyx in sage.symbolic.ring.SymbolicRing.var (build/cythonized/sage/symbolic/ring.cpp:10242)() 840 for s in names_list: 841 if not isidentifier(s): --> 842 raise ValueError('The name "'+s+'" is not a valid Python identifier.') 843 844 formatted_latex_name = None

ValueError: The name "+" is not a valid Python identifier.

edit retag flag offensive close merge delete

Comments

It seems Sage has trouble parsing the output from Maxima. Can you/someone try solving the same system in Maxima (with desolve I presume) and adding the output?

rburing ( 2018-08-30 10:08:30 +0100 )edit

This is the bug reported in https://trac.sagemath.org/ticket/23445. Unfortunately, it has not been fixed yet...

eric_g ( 2018-08-30 11:38:18 +0100 )edit

@Chernoxyl

To display blocks of code or error messages, skip a line above and below, and do one of the following (all give the same result):

indent all code lines with 4 spaces
select all code lines and click the "code" button (the icon with '101 010')
select all code lines and hit ctrl-K

For instance, typing

If we define `f` by

    def f(x, y, z):
        return x * y * z

then `f(2, 3, 5)` returns `30` but `f(2*3*5)` gives:

    TypeError: f() takes exactly 3 arguments (1 given)

produces:

If we define f by
def f(x, y, z):
    return x * y * z
then f(2, 3, 5) returns 30 but f(2*3*5) gives:
TypeError: f() takes exactly 3 arguments (1 given)

Please edit your question to do that.

slelievre ( 2018-09-01 00:01:46 +0100 )edit

add a comment

Bug in ODE solving?

Comments

Be the first one to answer this question!

Question Tools

Stats

Related questions

Bug in ODE solving? edit

Comments

Be the first one to answer this question!

Question Tools

Stats

Related questions

Bug in ODE solving?