# automatic substitution within functions?

what i do to do this?

sage: var('t w')
sage: f(t) = sin(w*t)
t |--> sin(t*w)
sage: w = 2
sage: f
t |--> sin(2*w)


Without doing f(w=2)!!! imagine that the function is f->f(a,b,c,d,f....,t) like doing this:

...
...
sage: aw1=aw1(m1=1,m2=0.5,l1=1,l2=0.5,g=9.8)
sage: aw2=aw2(m1=1,m2=0.5,l1=1,l2=0.5,g=9.8)
sage: aw4=aw4(m1=1,m2=0.5,l1=1,l2=0.5,g=9.8)
...
...


etc

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I think I'm just explaining Mike's answer a little, but I think that you should be able to define a dictionary

sage: params = {m1:1,m2:0.5,l1:1,l2:0.5,g:9.8}


and then do f.subs(params) as above. In his example,

var('t, w')
params = {w: 2,d:1,c:1}
f(a,b,c,d,e,f,g,t) = sin(t*w*d-c)
g=f.subs(params)
g


should do it. Mike, is that extra thing necessary, given that the arguments are the same in both cases?

more

hi, you can prefix the preformatted text with four space characters, then they will not wrap

( 2010-08-25 15:11:51 -0600 )edit

Okay, but then there should be much more information about the wiki formatting somewhere (FAQ?). Maybe even a little button for multiline code, sort of like the backticks for inline code? Sorry for us all requesting so many new things!

( 2010-08-25 15:15:34 -0600 )edit

You are right, we keep track of all these issues and will fix them. Thanks. Actually the button with a whole bunch of zeroes and ones helps format both multiline and inline code.

( 2010-08-25 15:38:18 -0600 )edit

Actually, you don't need. However, if you did f(w=2) then that doesn't return a CallableSymbolicExpression, but f.subs(params) does return one. I'll update my answer.

( 2010-08-25 16:02:35 -0600 )edit

i got it now, thanks

( 2010-08-25 16:54:59 -0600 )edit

The w in sin(t*w) does not refer to whatever the object with identifier w in the current scope. There isn't a way to get Python to work like this. You need to do something like:

sage: var('t, w')
(t, w)
sage: params = {w: 2}
sage: f(a,b,c,d,e,f,g,t) = sin(t*w)
sage: f.subs(params)
(a, b, c, d, e, f, g, t) |--> sin(2*t)
`

You just have to define the replacements you want once in a dictionary. You still have to call subs once for every function you want to change.

more

thanks, :( thats exactly what i don't want. what if f->f(a,b,c,d,f....,t)? it would be a little annoying to do that.

( 2010-08-25 12:14:15 -0600 )edit

I've updated my answer. Could you explain the annoying part? Do you mean having to do the ".function(*f.arguments())" part?

( 2010-08-25 12:20:11 -0600 )edit

i have updated my question, its about doing f(a=1,b=2,c=3...)

( 2010-08-25 12:32:44 -0600 )edit

( 2010-08-25 16:54:36 -0600 )edit

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