# Substitute an array of number for a symbolic variable

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David Arnold on 1 Nov 2012
Commented: Walter Roberson on 12 Jul 2019
Hi,
I have:
syms x y
f=x^3+y^3+3x^2+2y^2+9
fx=diff(f,x)
now, I'd like to substitute these two vectors of x and y values into the expression fx.
x=[1,2,3,4,5]
y=[6,7,8,9,10]
How do I do that with the subs command? If I can't do that with the subs command, what do you recommend?
David.
Star Strider on 1 Nov 2012
Question: Do you want a matrix with the function evaluation of fx for each value of (x,y) as an individual element?
What version of MATLAB do you have? Beginning with 2012a, symbolic functions are possible.

Walter Roberson on 1 Nov 2012
subs(fx, {x, y}, {[1,2,4,5,6}, [6,7,8,9,10]})
This syntax is documented relatively far down in the examples.
Walter Roberson on 12 Jul 2019
Thanks it works

Azzi Abdelmalek on 1 Nov 2012
syms x y
f=x^3+y^3+3*x^2+2*y^2+9
fx=diff(f,x)
x=[1,2,3,4,5]
y=[6,7,8,9,10]
eval(f)
eval(fx)

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