Hello,
Looking back at a previous thread
(http://groups.google.com/group/sympy/browse_thread/thread/a406176eeb28eb04),
an interesting procedure was discussed to place p[i,j,n+1] terms on the
LHS of the expression. (Thanks again, Aaron!) As shown in another
sample code below, the procedure uses as_independent() with filter and
lambda.
I am testing this example code with the main branch of sympy, and I
receive the following error:
Traceback (most recent call last):
File "test-collect-final.py", line 33, in <module>
main()
File "test-collect-final.py", line 29, in main
generate_fdtd(expr,n+1)
File "test-collect-final.py", line 21, in generate_fdtd
expr3 = expr2.as_independent(*filter(lambda t: t.args[-1] ==
Idx(n), expr2.atoms(IndexedBase) ) )
File "/usr/local/lib/python2.6/dist-packages/sympy/core/expr.py",
line 323, in as_independent
if term.has(*deps):
File "/usr/local/lib/python2.6/dist-packages/sympy/core/basic.py",
line 919, in has
raise TypeError("has() requires at least 1 argument (got none)")
TypeError: has() requires at least 1 argument (got none)
I understand that IndexedBase is now used instead of IndexedElement in
the main branch, and I am wondering if something has changed (or if I am
missing something again). What would I have to change to make this code
work with the main branch of sympy?
Nicholas
#begin sample code
from sympy import *
from sympy.tensor import Indexed, Idx, IndexedBase
from sympy.matrices import *
p = IndexedBase('p')
var('deltax deltay delta deltat A B')
i,j,n = symbols('i j n', integer = True)
#
# function to generate the FDTD scheme
#
# All p[i,j,n+1] indices should be collected and on the LHS of the
expression
def generate_fdtd(expr, nsolve):
expr0 = expr.lhs - expr.rhs
expr1 = expr0.expand()
w1 = Wild('w1',integer=True)
w2 = Wild('w2',integer=True)
expr2 = collect(expr1, p[w1, w2, nsolve])
expr3 = expr2.as_independent(*filter(lambda t: t.args[-1] ==
Idx(n), expr2.atoms(IndexedBase) ) ) # error here
right = -1 * expr3[0]
left = expr3[1]
return Eq(left, right.expand())
def main():
expr = Eq( A*p[1,1,n+1] - B*p[1,1,n], B*p[1,1,n+1] + A*p[1,2,n] +
B*p[1,2,n+1] + A*p[1,2,n+1])
generate_fdtd(expr,n+1)
if __name__ == "__main__":
main()
# end sample code
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