Implementing convolution using SymPy
I started using SymPy recently, and I implemented convolution using it.
def convolve(f,g,x,lower_limit,upper_limit):
y=Symbol('y')
h = g.subs(x,x-y)
return integrate(f*h,(y,lower_limit,upper_limit))
It seems to work for a few tests I've done.
Would like to know what you think of it, any improvements are appreciated.
python signal-processing sympy
edited Sep 1 '17 at 12:57
200_success
128k15150412
asked Sep 1 '17 at 9:23
Itay4
405
add a comment |
I started using SymPy recently, and I implemented convolution using it.
def convolve(f,g,x,lower_limit,upper_limit):
y=Symbol('y')
h = g.subs(x,x-y)
return integrate(f*h,(y,lower_limit,upper_limit))
It seems to work for a few tests I've done.
Would like to know what you think of it, any improvements are appreciated.
python signal-processing sympy
edited Sep 1 '17 at 12:57
200_success
128k15150412
asked Sep 1 '17 at 9:23
Itay4
405
add a comment |
I started using SymPy recently, and I implemented convolution using it.
def convolve(f,g,x,lower_limit,upper_limit):
y=Symbol('y')
h = g.subs(x,x-y)
return integrate(f*h,(y,lower_limit,upper_limit))
It seems to work for a few tests I've done.
Would like to know what you think of it, any improvements are appreciated.
python signal-processing sympy
edited Sep 1 '17 at 12:57
200_success
128k15150412
asked Sep 1 '17 at 9:23
Itay4
405
I started using SymPy recently, and I implemented convolution using it.
def convolve(f,g,x,lower_limit,upper_limit):
y=Symbol('y')
h = g.subs(x,x-y)
return integrate(f*h,(y,lower_limit,upper_limit))
It seems to work for a few tests I've done.
Would like to know what you think of it, any improvements are appreciated.
python signal-processing sympy
python signal-processing sympy
edited Sep 1 '17 at 12:57
200_success
128k15150412
asked Sep 1 '17 at 9:23
Itay4
405
edited Sep 1 '17 at 12:57
200_success
128k15150412
asked Sep 1 '17 at 9:23
Itay4
405
edited Sep 1 '17 at 12:57
200_success
128k15150412
edited Sep 1 '17 at 12:57
200_success
128k15150412
edited Sep 1 '17 at 12:57
200_success
128k15150412
128k15150412
asked Sep 1 '17 at 9:23
Itay4
405
asked Sep 1 '17 at 9:23
Itay4
405
asked Sep 1 '17 at 9:23
Itay4
405
405
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
Problematic Assumptions
You implicitly assume that x is not Symbol('y'). If it is, then g.subs(x, x-y) will return a different, constant function (g'(x) = g(0)). You could check for this case and handle it specially, or just use a more uncommon symbol to reduce the risk.
Formatting
You have inconsistent spacing in your code. PEP8 recommends a space after every comma and on either side of binary operators (like =, -, and *):
def convolve(f, g, x, lower_limit, upper_limit):
y = Symbol('y')
h = g.subs(x, x - y)
return integrate(f * h, (y, lower_limit, upper_limit))
answered Sep 7 '17 at 3:01
Mego
20627
add a comment |
Your code shouldn't work:
You are calculating:
$$int_a^b f(t) , g(t - tau) ; dtau$$
but convolution is defined as:
$$f(t) , * , g(t) equiv int_{-infty}^{infty} f(tau) , g(t - tau) ; dtau$$
so the default limits of integration should be $-infty$ to $infty$. More importantly you should use the proper argument for f (the integration variable). Finally, naming the integration variable y feels unusual.
from sympy import oo, Symbol, integrate
def convolve(f, g, t, lower_limit=-oo, upper_limit=oo):
tau = Symbol('__very_unlikely_name__', real=True)
return integrate(f.subs(t, tau) * g.subs(t, t - tau),
(tau, lower_limit, upper_limit))
answered Aug 27 at 21:10
JakeI
313
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Problematic Assumptions
You implicitly assume that x is not Symbol('y'). If it is, then g.subs(x, x-y) will return a different, constant function (g'(x) = g(0)). You could check for this case and handle it specially, or just use a more uncommon symbol to reduce the risk.
Formatting
You have inconsistent spacing in your code. PEP8 recommends a space after every comma and on either side of binary operators (like =, -, and *):
def convolve(f, g, x, lower_limit, upper_limit):
y = Symbol('y')
h = g.subs(x, x - y)
return integrate(f * h, (y, lower_limit, upper_limit))
answered Sep 7 '17 at 3:01
Mego
20627
add a comment |
Problematic Assumptions
You implicitly assume that x is not Symbol('y'). If it is, then g.subs(x, x-y) will return a different, constant function (g'(x) = g(0)). You could check for this case and handle it specially, or just use a more uncommon symbol to reduce the risk.
Formatting
You have inconsistent spacing in your code. PEP8 recommends a space after every comma and on either side of binary operators (like =, -, and *):
def convolve(f, g, x, lower_limit, upper_limit):
y = Symbol('y')
h = g.subs(x, x - y)
return integrate(f * h, (y, lower_limit, upper_limit))
answered Sep 7 '17 at 3:01
Mego
20627
add a comment |
Problematic Assumptions
You implicitly assume that x is not Symbol('y'). If it is, then g.subs(x, x-y) will return a different, constant function (g'(x) = g(0)). You could check for this case and handle it specially, or just use a more uncommon symbol to reduce the risk.
Formatting
You have inconsistent spacing in your code. PEP8 recommends a space after every comma and on either side of binary operators (like =, -, and *):
def convolve(f, g, x, lower_limit, upper_limit):
y = Symbol('y')
h = g.subs(x, x - y)
return integrate(f * h, (y, lower_limit, upper_limit))
answered Sep 7 '17 at 3:01
Mego
20627
Problematic Assumptions
You implicitly assume that x is not Symbol('y'). If it is, then g.subs(x, x-y) will return a different, constant function (g'(x) = g(0)). You could check for this case and handle it specially, or just use a more uncommon symbol to reduce the risk.
Formatting
You have inconsistent spacing in your code. PEP8 recommends a space after every comma and on either side of binary operators (like =, -, and *):
def convolve(f, g, x, lower_limit, upper_limit):
y = Symbol('y')
h = g.subs(x, x - y)
return integrate(f * h, (y, lower_limit, upper_limit))
answered Sep 7 '17 at 3:01
Mego
20627
answered Sep 7 '17 at 3:01
Mego
20627
answered Sep 7 '17 at 3:01
Mego
20627
answered Sep 7 '17 at 3:01
Mego
20627
20627
add a comment |
add a comment |
Your code shouldn't work:
You are calculating:
$$int_a^b f(t) , g(t - tau) ; dtau$$
but convolution is defined as:
$$f(t) , * , g(t) equiv int_{-infty}^{infty} f(tau) , g(t - tau) ; dtau$$
so the default limits of integration should be $-infty$ to $infty$. More importantly you should use the proper argument for f (the integration variable). Finally, naming the integration variable y feels unusual.
from sympy import oo, Symbol, integrate
def convolve(f, g, t, lower_limit=-oo, upper_limit=oo):
tau = Symbol('__very_unlikely_name__', real=True)
return integrate(f.subs(t, tau) * g.subs(t, t - tau),
(tau, lower_limit, upper_limit))
answered Aug 27 at 21:10
JakeI
313
add a comment |
Your code shouldn't work:
You are calculating:
$$int_a^b f(t) , g(t - tau) ; dtau$$
but convolution is defined as:
$$f(t) , * , g(t) equiv int_{-infty}^{infty} f(tau) , g(t - tau) ; dtau$$
so the default limits of integration should be $-infty$ to $infty$. More importantly you should use the proper argument for f (the integration variable). Finally, naming the integration variable y feels unusual.
from sympy import oo, Symbol, integrate
def convolve(f, g, t, lower_limit=-oo, upper_limit=oo):
tau = Symbol('__very_unlikely_name__', real=True)
return integrate(f.subs(t, tau) * g.subs(t, t - tau),
(tau, lower_limit, upper_limit))
answered Aug 27 at 21:10
JakeI
313
add a comment |
Your code shouldn't work:
You are calculating:
$$int_a^b f(t) , g(t - tau) ; dtau$$
but convolution is defined as:
$$f(t) , * , g(t) equiv int_{-infty}^{infty} f(tau) , g(t - tau) ; dtau$$
so the default limits of integration should be $-infty$ to $infty$. More importantly you should use the proper argument for f (the integration variable). Finally, naming the integration variable y feels unusual.
from sympy import oo, Symbol, integrate
def convolve(f, g, t, lower_limit=-oo, upper_limit=oo):
tau = Symbol('__very_unlikely_name__', real=True)
return integrate(f.subs(t, tau) * g.subs(t, t - tau),
(tau, lower_limit, upper_limit))
answered Aug 27 at 21:10
JakeI
313
Your code shouldn't work:
You are calculating:
$$int_a^b f(t) , g(t - tau) ; dtau$$
but convolution is defined as:
$$f(t) , * , g(t) equiv int_{-infty}^{infty} f(tau) , g(t - tau) ; dtau$$
so the default limits of integration should be $-infty$ to $infty$. More importantly you should use the proper argument for f (the integration variable). Finally, naming the integration variable y feels unusual.
from sympy import oo, Symbol, integrate
def convolve(f, g, t, lower_limit=-oo, upper_limit=oo):
tau = Symbol('__very_unlikely_name__', real=True)
return integrate(f.subs(t, tau) * g.subs(t, t - tau),
(tau, lower_limit, upper_limit))
answered Aug 27 at 21:10
JakeI
313
edited 24 mins ago
answered Aug 27 at 21:10
JakeI
313
answered Aug 27 at 21:10
JakeI
313
answered Aug 27 at 21:10
JakeI
313
313
add a comment |
add a comment |
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