Aaron S. Meurer wrote:
On Jun 13, 2010, at 11:25 AM, Alan Bromborsky wrote:
Aaron S. Meurer wrote:
Wouldn't you just use the .subs() method, or does that not work?
Aaron Meurer
On Jun 13, 2010, at 6:57 AM, Alan Bromborsky wrote:
How would I do the following:
I have a generic function: d_1 = Function('d_1')(x)
that I apply to another function f in an expression such as y = 5*x_1**2+d_1(f).
Later I wish to substitute an explicit function such as
def D_1(f):
return(diff(f,x_1))
for d_1 and have y expanded after the substitution. For example if f =
x_1**2+x_2**2 then
y = 5*x_1**2+2*x_1
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I tried this:
from sympy import *
x = Symbol('x')
x_1 = Symbol('x_1')
x_2 = Symbol('x_2')
def df_1(F):
global x_1
return(diff(F,x_1))
if __name__ == '__main__':
F = Function('df')(x)
y = x_1**2+x_2**2
z = y+F(y)
print z
and got:
Traceback (most recent call last):
File "testtensor.py", line 26, in <module>
z = y+F(y)
File
"/usr/local/lib/python2.6/dist-packages/sympy-0.6.7_git-py2.6.egg/sympy/core/basic.py",
line 1310, in __call__
raise TypeError("argument must be a dictionary")
TypeError: argument must be a dictionary
I must be missing something. I haven't even tried to substitute yet.
What are you trying to do with F(y)? You have df is a Function and F = df(x),
and you are trying to apply the function twice, df(x)(y), which is not allowed.
I think maybe you really mean to just have F = Function('df').
Aaron Meurer
I input:
from sympy import *
x_1 = Symbol('x_1')
x_2 = Symbol('x_2')
df = Function('df')
diff_flg = False
def df_1(F):
global x_1,diff_flg
if diff_flg:
return(diff(F,x_1))
else:
return(df(F))
if __name__ == '__main__':
x = Symbol('x')
df = Function('df')
print df
y = x_1**2+x_2**2
print x,x_1,x_2,y
z = y + df_1(y)
print z
and got:
df
x x_1 x_2 x_1**2 + x_2**2
df(x_1**2 + x_2**2) + x_1**2 + x_2**2
Now the question is if I then set diff_flg=True is there a way to
recalculate z so that z = 2*x_1+x_1**2+x_2**2 is returned.
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