solve multiple equation in one variable

7 次查看（过去 30 天）
Kalvin
Kalvin 2022-10-28
编辑： Torsten 2022-10-28
syms p1 p2 p3 p4 p5
B = [(75*p2)/2 - (153*p3)/4 + (199*p4)/6 + (31*p5)/12 - 2165/12 == -433/36, 58*p2 - (89*p3)/2 + (457*p4)/9 + (127*p5)/18 - 4763/18 == -433/36, 38*p2 - (59*p3)/2 + (344*p4)/9 + (161*p5)/18 - 3031/18 == -433/36, 70*p2 - 81*p3 + (625*p4)/9 + (125*p5)/9 - 3031/9 == -433/36, (89*p2)/2 - (225*p3)/4 + (841*p4)/18 - (11*p5)/36 - 9959/36 == -433/36]
solve(b)
solx = [ans.p2 ans.p3 ans.p4 ans.p5]
i got 5 equation in B variable but when im trying to solve it. it always show
p2 = [0x1 sym]
p3 = [0x1 sym]
p4 = [0x1 sym]
p5 = [0x1 sym]
empty sym; 0 - by-4
is there any solution to solve that equation?
thank you

请先登录，再回答此问题。

采纳的回答

Davide Masiello
Davide Masiello 2022-10-28
编辑：Davide Masiello 2022-10-28
Ran in:
I think the problem is that you have 5 equations and 4 variables, because p1 does not appear anywhere in the system.
Therefore the system is overdetermined.
If I try to solve canceling the last equation it works, see below
syms p1 p2 p3 p4 p5
B = [(75*p2)/2 - (153*p3)/4 + (199*p4)/6 + (31*p5)/12 - 2165/12 == -433/36; 58*p2 - (89*p3)/2 + (457*p4)/9 + (127*p5)/18 - 4763/18 == -433/36; 38*p2 - (59*p3)/2 + (344*p4)/9 + (161*p5)/18 - 3031/18 == -433/36; 70*p2 - 81*p3 + (625*p4)/9 + (125*p5)/9 - 3031/9 == -433/36] % (89*p2)/2 - (225*p3)/4 + (841*p4)/18 - (11*p5)/36 - 9959/36 == -433/36]
B = 
s = solve(B)
s = struct with fields:
p2: 122537701/16461144 p3: -1231019/783864 p4: -1665751/304836 p5: 7365763/1829016
Are you sure the system is correctly coded?
You might have missed to include p1 somewhere.
  2 个评论
Kalvin
Kalvin 2022-10-28
编辑：Kalvin 2022-10-28
I see. So is there any command that can erase 1 equation from that variable? The p1 is missing because i need to substitude the p1 with another equation. Thats why i need to erase one equation from that variable.
Torsten
Torsten 2022-10-28
编辑：Torsten 2022-10-28
Ran in:
syms p1 p2 p3 p4 p5
B = [(75*p2)/2 - (153*p3)/4 + (199*p4)/6 + (31*p5)/12 - 2165/12 == -433/36, 58*p2 - (89*p3)/2 + (457*p4)/9 + (127*p5)/18 - 4763/18 == -433/36, 38*p2 - (59*p3)/2 + (344*p4)/9 + (161*p5)/18 - 3031/18 == -433/36, 70*p2 - 81*p3 + (625*p4)/9 + (125*p5)/9 - 3031/9 == -433/36, (89*p2)/2 - (225*p3)/4 + (841*p4)/18 - (11*p5)/36 - 9959/36 == -433/36]
B = 
s = solve([B(1),B(3),B(4),B(5)]); % e.g.
p2 = double(s.p2)
p2 = -0.9168
p3 = double(s.p3)
p3 = -1.1433
p4 = double(s.p4)
p4 = 5.1320
p5 = double(s.p5)
p5 = -4.3249
or use
[A,b] = equationsToMatrix(B);
sol = double(A)\double(b)
sol = 4×1
0.8276 -0.6442 4.0401 -4.8917
which solves the system of 5 equations in 4 unknowns in the least-squares sense.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Linear Algebra 的更多信息

标签

产品


版本

R2021a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by