Issues with subs function

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Alejandro Noriega Soto
编辑： Paul 2023-4-9
Ran in:
Hi, I'm doing some stuff with structural analysis and I need to substitute a symbolic variable in a symbolic funtion, but it seems that matlab substitutes all the variables when i need just to change one of them, then, the resulting expression must have one of the variables, but that does not happen ¿Could someone help me please?
l1=3;
h1=1.45;
b1=sqrt(l1^2+h1^2);
z=atand(h1/l1);
q1 = 0;
syms r1v x
R2v(r1v) =r1v/3 - 209/1395;
Mz1v(r1v,x) = -r1v + (R2v(r1v) * cosd(z)) * x + (q1 * sind(z)) * x
Mz1v(r1v, x) = 
subs(Mz1v,x,b1)
ans(r1v, x) = 
The expected ouput should have an expression in terms of r1v because i'm just changing the value of x but it does not happen

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采纳的回答

Paul
Paul 2023-4-9
编辑：Paul 2023-4-9
Ran in:
I'm sure if you go through it step-by-step, or w/o assigning numbers until the end, you'll see that value of b1 is magical and all of the terms in r1v go away
l1=3;
h1=1.45;
syms l1 h1 real
b1=sqrt(l1^2+h1^2);
z=atand(h1/l1);
q1 = 0;
syms r1v x
R2v(r1v) =r1v/3 - 209/1395;
Mz1v(r1v,x) = -r1v + (R2v(r1v) * cosd(z)) * x + (q1 * sind(z)) * x
Mz1v(r1v, x) = 
Mz1v = simplify(Mz1v)
Mz1v(r1v, x) = 
Mz1v(r1v,b1)
ans = 
If l1 = 3, as in this case, then the r1v is annihilated, and we're left with
subs(ans,l1,3)
ans = 

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