symbolic array, zero-based elements into another array

if I have the following matrix:

   syms x11 x21 x31 x41

a = [ 1*x11  2*x21  3*x31  3*x41]

b = [ 1*x11  2*x21  3*x41]

I want to generate a array which is c:

c = [1*x11  2*x21  0 3*x41]

is easy to do this however does not touch time with sym then forgot.

Thanks in advance.

Answer 1

[Walter Roberson]

I do not understand your line about "does not touch time with sym then forgot".

c = a;
c(a == sum(a) - sum(b)) = 0;

You might perhaps want to describe the variable possibilities in more detail if the above is not the answer.

Answer 2

[Andrei Bobrov]

syms x11 x21 x31 x41
a = [ 1*x11  2*x21  3*x31  3*x41]
b = [ 1*x11  2*x21  3*x41]
c = a.*ismember(a,b)

[Artur M. G. Lourenço]

Your answer is correct.

Answer 3

[Artur M. G. Lourenço]

Thank you for all