Matlab don't show calculated variables.

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Tiago Araujo
Tiago Araujo 2021-4-13
编辑： Walter Roberson 2021-4-14
I wrote this:
syms C0 C1 C2 C3 X L P EI1 EI2
Y(X)=C0+C1*X+C2*X^2+C3*X^3;
dY(X)=diff(Y(X),X);
d2Y(X)=diff(dY(X),X);
f0 = Y(0) == 0;
f1 = Y(L) == 0;
R=solve([f0,f1],[C0,C1]);
C0 = R.C0;
C1 = R.C1;
U=(EI1/2)*int(d2Y(X)^2,[0 L/2])+(EI2/2)*int(d2Y(X)^2,[L/2 L]);
V=-P*Y(L/2);
PI(C2,C3)=U+V;
dPIdC2=diff(PI(C2,C3),C2);
dPIdC3=diff(PI(C2,C3),C3);
f2 = dPIdC2 == 0;
f3 = dPIdC3 == 0;
S=solve([f2,f3],[C2,C3]);
C2 = S.C2;
C3 = S.C3;
C= ([C0;C1;C2;C3]);
disp(C);
Y(X)=C0+C1*X+C2*X^2+C3*X^3;
disp Y(X);
disp (Y(X));
FLECHA = Y(L/2)
But Matlab returns:
C =
0
- C3*L^2 - C2*L
(P*(EI1*L + 11*EI2*L))/(4*(EI1^2 + 14*EI1*EI2 + EI2^2))
-(P*(EI1 + 7*EI2))/(6*(EI1^2 + 14*EI1*EI2 + EI2^2))
______________________________________________
Y(X)
C3*X^3 + C2*X^2 + C1*X + C0
FLECHA
(C3*L^3)/8 + (C2*L^2)/4 + (C1*L)/2 + C0
It dont show Y(X) in terms of calculated values of C0, C1, C2 and C3.
I Want the Y(x) in function of P, L, EI1, EI2, (...), with this script these variables C0, C1... are calculateds but MATLAB dont write Y(X) em terms of them.

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采纳的回答

Tiago Araujo
Tiago Araujo 2021-4-14
编辑：Walter Roberson 2021-4-14
I fixed doing:
syms C0 C1 C2 C3 X L P EI1 EI2
Y(X)=C0+C1*X+C2*X^2+C3*X^3;
dY(X)=diff(Y(X),X);
d2Y(X)=diff(dY(X),X);
f0 = Y(0) == 0;
f1 = Y(L) == 0;
U=(EI1/2)*int(d2Y(X)^2,[0 L/2])+(EI2/2)*int(d2Y(X)^2,[L/2 L]);
V=-P*Y(L/2);
PI(C2,C3)=U+V;
dPIdC2=diff(PI(C2,C3),C2);
dPIdC3=diff(PI(C2,C3),C3);
f2 = dPIdC2 == 0;
f3 = dPIdC3 == 0;
S=solve([f0,f1,f2,f3],[C0,C1,C2,C3]);
C0=S.C0;
C1=S.C1;
C2 = S.C2;
C3 = S.C3;
C= ([C0;C1;C2;C3]);
disp(C);
Y(X)=C0+C1*X+C2*X^2+C3*X^3;
disp Y(X);
disp (Y(X));
FLECHA = Y(L/2)

更多回答（1 个）

Jan
Jan 2021-4-14
Ran in:
I get a dfifferent output than you:
syms C0 C1 C2 C3 X L P EI1 EI2
Y(X)=C0+C1*X+C2*X^2+C3*X^3;
dY(X)=diff(Y(X),X);
d2Y(X)=diff(dY(X),X);
f0 = Y(0) == 0;
f1 = Y(L) == 0;
R=solve([f0,f1],[C0,C1]);
C0 = R.C0;
C1 = R.C1;
U=(EI1/2)*int(d2Y(X)^2,[0 L/2])+(EI2/2)*int(d2Y(X)^2,[L/2 L]);
V=-P*Y(L/2);
PI(C2,C3)=U+V;
dPIdC2=diff(PI(C2,C3),C2);
dPIdC3=diff(PI(C2,C3),C3);
f2 = dPIdC2 == 0;
f3 = dPIdC3 == 0;
S=solve([f2,f3],[C2,C3]);
C2 = S.C2;
C3 = S.C3;
C= ([C0;C1;C2;C3]);
disp(C);
Y(X)=C0+C1*X+C2*X^2+C3*X^3;
disp Y(X);
Y(X)
disp (Y(X));
FLECHA = Y(L/2)
FLECHA = 
  1 个评论
Tiago Araujo
Tiago Araujo 2021-4-14
Hi! Thanks!
But, have you seen that the C3 and C2 are still present in the Y(X) instead of their value in function of EI, P and L... ?
I need Y(X) only in function of EI1 EI2 P and L...

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