how can a symbolic derivative be vectorized automatically?

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Marko
Marko 2023-10-20
回答： Walter Roberson 2023-10-20
Hello,
here is the simplified problem.
I have a symblic function with three arguments. And the derivative of f wrt. b
syms a b c
f = a*sin(b)*exp(c)
df = diff(f,b)
The solution is:
df = a*exp(c)*cos(b)
Now i will use this derivatve in a numeric script. And the argumetns a,b,c are vectors:
a=rand(10,1);
b=rand(10,1);
c=rand(10,1);
My current approach is to modify the derivative manualy: (adding "dots")
df = a.*exp(c).*cos(b)
Is there a way how i can change a symblic expression automatically?
My equations are has 80 or more characters and the derivatives has 2x to 3x the amount of characters.
So an automatic transform into an vectorized version would help me a lot.
Best regards,
MJ

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采纳的回答

Stephen23
Stephen23 2023-10-20
Ran in:
Use MATLABFUNCTION:
syms a b c
f = a*sin(b)*exp(c)
f = 
df = diff(f,b)
df = 
mf = matlabFunction(df)
mf = function_handle with value:
@(a,b,c)a.*exp(c).*cos(b)
a=rand(10,1);
b=rand(10,1);
c=rand(10,1);
mf(a,b,c)
ans = 10×1
0.8287 0.4912 0.5251 2.2295 1.7548 0.0752 1.3973 0.6642 0.1812 0.5342

更多回答（2 个）

Dyuman Joshi
Dyuman Joshi 2023-10-20
Ran in:
Convert it to a function handle -
syms a b c
f = a*sin(b)*exp(c)
f = 
df = diff(f,b)
df = 
%Convert the symbolic function to an anonymous function
fun = matlabFunction(df)
fun = function_handle with value:
@(a,b,c)a.*exp(c).*cos(b)
a=rand(10,1);
b=rand(10,1);
c=rand(10,1);
fun(a,b,c)
ans = 10×1
1.6337 0.7283 1.9453 1.1977 0.0795 1.0797 0.8060 0.3090 2.5127 0.9578
Walter Roberson
Walter Roberson 2023-10-20
Ran in:
format long g
syms a b c
f(a,b,c) = a*sin(b)*exp(c)
f(a, b, c) = 
df = diff(f,b)
df(a, b, c) = 
A = rand(10,1);
B = rand(10,1);
C = rand(10,1);
D = df(A, B, C)
D = 
vpa(D)
ans = 
double(D)
ans = 10×1
0.472553502790635 1.26659066678776 0.609162623765823 0.642273629496948 0.893411797110293 0.88743081840584 0.39637226337217 0.303468357868928 0.198740877661276 1.09526181869221

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