Need help substituting vector variables into symbolic expression

Hello!

I have a symbolic expression into which I would like to substitute two vector variables:

syms x w1 b1
l1 = tanh(x * w1 + b1);
w1_actual = rand(1,10);
temp = subs(l1,w1,w1_actual);

This correctly generates a 1x10 symbolic array, but when performing the second substitution:

b1_actual = zeros(1,10);
l1_sym = subs(temp,b1,b1_actual);

This generates a 1x100 symbolic array because the 1x10 vector is expanded in each element.

I want the result of both substitutions to yield a 1x10 array, as is the case for the expression:

l1 = x * w1_actual + b1_actual;

I tried making both substitutions simultaneously:

l1 = subs(l1,[w1,b1],[w1_actual,b1_actual]);

but this resulted in the error:

Inconsistency between sizes of second and third arguments.

I also tried declaring the symbols as symmatrices:

syms x [1 1] matrix
syms w1 [1 10] matrix
syms b1 [1 10] matrix

But this prevents subs() from performing any substitutions for either the w1 and b1 variables.

Thank you in advance!

[Aquatris]

Seems to work fine however when substituting matrices, you need to clarify where a matrix starts and ends, which is done via cell arrays

syms x w1 b1
l1 = tanh(x * w1 + b1);
w1_actual = rand(1,10);
b1_actual = zeros(1,10);
temp = subs(l1,[w1 b1],{w1_actual,  b1_actual});
size(temp)

ans = 1×2

1 10

Answer 1

[Paul]

syms x y

Option 1. Use a symbolic function

z(x,y) = x + y

z(x, y) = 

z([1 2],[100 200])

ans = 

Option 2. Symbolic expression, subs with a cell array

z = x + y;
subs(z,{x y},{[1 2],[100 200]})

ans = 

Answer 2

[Torsten]

syms x w1 b1
l1 = tanh(x * w1 + b1);
b1_actual = zeros(1,10);
w1_actual = rand(1,10);
l1_actual = arrayfun(@(i)subs(l1,[w1,b1],[w1_actual(i),b1_actual(i)]),1:10)

l1_actual = 

Answer 3

[Star Strider]

I may be missing something in your problem statement.

Is this what you want to do —

syms x w1 b1
l1 = tanh(x * w1 + b1);
w1_actual = randi(9,1,10)

w1_actual = 1×10

4 7 9 3 9 1 9 9 2 1

b1_actual = randi(9,1,10)

b1_actual = 1×10

1 4 4 9 6 2 5 8 3 8

temp = subs(l1,{w1,b1},{w1_actual,b1_actual})

temp = 

.