[sage-support] Re: How to replace variables in function?
Try this instead:
# just as you had before:
r=2*2*pi
Pole1=r*exp(I*2*pi/3)
Pole2=-r
Pole3=r*exp(-I*2*pi/3)
Ts=0.1
# one change here:
var('f')
z=exp(I*2*pi*Ts*f)
p=(2/Ts)*(z-1)/(z+1)
H = (p^3)/((p-Pole1)*(p-Pole2)*(p-Pole3))
Then H (or show(H)) will print out a complicated expression in terms
of f, and
H.subs(f=3)
will plug in f=3.
H.subs(f=3).n(4)
will gives a decimal approximation to H.subs(f=3) to 4 bits of
precision.
H.subs(f=3).n(digits=12)
will give an approximation to 12 decimal digits of precision.
Or, as Tim Lahey hints, you could define a function:
HH(x) = (x^3)/((x-Pole1)*(x-Pole2)*(x-Pole3))
Then 'HH(p)' will return the same thing as 'H' does.
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[sage-support] Re: How to replace variables in function?
Thank you! Than you all so much! It was so difficult to continue my research without it! And I am so glad Sage project have real support :-) --~--~-~--~~~---~--~~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~--~~~~--~~--~--~---
[sage-support] Re: How to replace variables in function?
(Sorry if this reply appears twice - 1st one disappeared?) This worked for me: - H, p, Pole1, Pole2, Pole3, Ts, z, f = var(H p Pole1 Pole2 Pole3 Ts z f) p = (2/Ts)*(z-1)/(z+1) z = exp(I*2*pi*Ts*f) H = (p^3)/((p-Pole1)*(p-Pole2)*(p-Pole3)) show(H) The only difference is that I have declared the variables in the first line. Hope that helps. On Dec 8, 5:58 pm, Sand Wraith [EMAIL PROTECTED] wrote: Hi all! Please help me to replace variables: I have this function: H(p)=(p^3)/((p-Pole1)*(p-Pole2)*(p-Pole3)) where Pole1,Pole2,Pole3 - complex: r=2*2*pi Pole1=r*exp(I*2*pi/3) Pole2=-r Pole3=r*exp(-I*2*pi/3) Ts=0.1 And I need to make a few replaces: need to replace p with (2/Ts)*(z-1)/(z+1), where z is a new variable, and then replace z with exp(I*2*pi*Ts*f). To have H(f) function at the end. I am trying to write: z=exp(I*2*pi*Ts*f) p=(2/Ts)*(z-1)/(z+1) H=(p^3)/((p-Pole1)*(p-Pole2)*(p-Pole3)) and now if I want to look at H: H or show(H) I've got many errors... tail of long output: sage-display stdin:16:Incorrect syntax: Syntax error _tmp_ : (8000.0( ^ sage-display(%o90) what is wrong with it? --~--~-~--~~~---~--~~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~--~~~~--~~--~--~---
