How would I use fsolve for 3 unknowns and 3 equations?

Question

David Magana 2022-5-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1728625-how-would-i-use-fsolve-for-3-unknowns-and-3-equations

评论： Star Strider 2022-5-29

I'm confused on how to use fsolve when solving for "TT, a_1, b_1" in my code. I'm trying to solve for each of these variables using the 3 equations that are supposed to be in a 3x1 matrix which is set equal to 'equations.' Any help is much appreciated.

clear;clc;format long;
lm1=0; %m
lm2=-0.2; %m
Am=95; %m^2
At=3; %m^2
omega_m=40.2; %1/s
omega_t=228; %1/s
p=1.225; %kg/m^3
w=32000; %N
hm=0.96; %m
lt=6.5; %m
ht=0.72; %m
equations=@(TT a_1 b_1) [lm1*w+hm*w*a_1-1/Qt*sqrt(TT^3/2*p*At)-1/Qm*sqrt(w^3/2*p*Am)*b_1);hm*w*b_1+(ht*TT)+(1/Qm)*sqrt(w^3/2*p*Am)*a_1;1/Qm*sqrt(w^3/2*p*Am)-lt*TT+lm1*w*b_1];
equationsans=fsolve(equations,[1,1,1]');
Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other syntax error. To construct matrices, use brackets instead of parentheses.

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Answer 1

Star Strider 2022-5-27

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1728625-how-would-i-use-fsolve-for-3-unknowns-and-3-equations#answer_973025

在 MATLAB Online 中打开

Provide values for ‘Qt’ and ‘Qm’ and then solve it —

clear;clc;format long;
lm1=0; %m
lm2=-0.2; %m
Am=95; %m^2
At=3; %m^2
omega_m=40.2; %1/s
omega_t=228; %1/s
p=1.225; %kg/m^3
w=32000; %N
hm=0.96; %m
lt=6.5; %m
ht=0.72; %m
Qm = rand
Qm = 
   0.770819305637386
Qt = rand
Qt = 
   0.909584161538862
equations=@(TT, a_1, b_1) [(lm1*w+hm*w*a_1-1/Qt*sqrt(TT^3/2*p*At)-1/Qm*sqrt(w^3/2*p*Am)*b_1);hm*w*b_1+(ht*TT)+(1/Qm)*sqrt(w^3/2*p*Am)*a_1;1/Qm*sqrt(w^3/2*p*Am)-lt*TT+lm1*w*b_1];
equationsans=fsolve(@(b)equations(b(1),b(2),b(3)),[1,1,1]')
Solver stopped prematurely.

fsolve stopped because it exceeded the function evaluation limit,
options.MaxFunctionEvaluations = 3.000000e+02.
equationsans = 3×1
1.0e+06 *

   4.838264690667167
   0.000000090313456
  -0.000279936800090