0 个投票

I am working with symbolic vector of 1xN size. The vector contains N eqations in the from of
X == a + b + c
Y == X*(d + e + f)
Z == Y + X
I am suing subs to substitute the coefficients a b c d e f with numeric values. The result is in the form of
X == g
Y ==X*h
Z == Y +X
It sould be quite straigh forward to solve for Z since all variables are numeric, but for crying out loud I cannot make matlab to solve for Z.
Any ideas?

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Torsten
Torsten 2024-6-30
Please include your code so far.
Kristian Dimitrov
Kristian Dimitrov 2024-6-30
编辑：Kristian Dimitrov 2024-6-30
This are the type of inputs that i am using
syms a b c d e
eqn = transpose(str2sym("[X == a+b+c, Y == X*(d+e), Z == X+Y]"));
eqn_S = subs(eqn,{a,b,c,d,e},{[1 2 3 4 5]});
and the outout i am getting
eqn_S =
X == 6
Y == 9*X
Z == X + Y
I tried vpa solve etc. but cannot find syntaxis that works properly to solve for Z.
One way i tried to solve it to solve each row separately and substitute its value in the following equations, but there must be more elegant solution to the problem.

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Kristian Dimitrov
Kristian Dimitrov 2024-6-30

1 个投票

vpasolve works perfetcly to solve it numerically.
syms a b c d e
eqn = transpose(str2sym("[X == a+b+c, Y == X*(d+e), Z == X+Y]"));
eqn_S = subs(eqn,{a,b,c,d,e},{[1 2 3 4 5]});
vpasolve(eqn_S)

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Torsten
Torsten 2024-6-30
编辑：Torsten 2024-6-30
Ran in:
Ran in:
syms a b c d e X Y Z
eqn = transpose(str2sym("[X == a+b+c, Y == X*(d+e), Z == X+Y]"))
eqn = 
sol = solve(eqn,[X,Y,Z]);
sol = struct with fields:
X: a + b + c Y: (d + e)*(a + b + c) Z: a + b + c + a*d + a*e + b*d + b*e + c*d + c*e
sol.Z = simplify(sol.Z)
sol = struct with fields:
X: a + b + c Y: (d + e)*(a + b + c) Z: (d + e + 1)*(a + b + c)
subs(sol,[a,b,c,d,e],[1,2,3,4,5])
ans = struct with fields:
X: 6 Y: 54 Z: 60

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