How can I get maximum and minimum value with sym variables

Question

Gookki Jeong 2020-7-30

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/572713-how-can-i-get-maximum-and-minimum-value-with-sym-variables

回答： madhan ravi 2020-7-30

clear; clc; close all;
syms seta
gamma = 1;
Rx_ = 1;
Ry_ = Rx_*gamma;
% 등가 정적 적용
gamma = 1;
Rx1= ( cos(seta)-0.3*sin(seta) )*Rx_ ;
Rx2= ( cos(seta)+0.3*sin(seta) )*Rx_;
Rx3= ( 0.3*cos(seta)-sin(seta) )*Rx_;
Rx4= ( -0.3*cos(seta)-sin(seta) )*Rx_;
Ry1= (0.3*cos(seta) + sin(seta) )*Ry_;
Ry2= (-0.3*cos(seta) + sin(seta) )*Ry_;
Ry3= (cos(seta) + 0.3*sin(seta) )*Ry_;
Ry4= (cos(seta) - 0.3*sin(seta) )*Ry_;
N=4;
for ii=1:N
   temp=['RR',num2str(ii),'=Rx',num2str(ii),'+Ry',num2str(ii),';'];
   eval(temp);
 end

here is my code, then I get

RR1 =
 (13*cos(seta))/10 + (7*sin(seta))/10
 
RR2 =
 (7*cos(seta))/10 + (13*sin(seta))/10

etc.

and now I want to get the max and min value and seta value at that point. but I don't know how I get it. the max(), min() didn't work for syms funtion.

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Answer 1

madhan ravi 2020-7-30

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/572713-how-can-i-get-maximum-and-minimum-value-with-sym-variables#answer_472870

在 MATLAB Online 中打开

Use matlabFunction() and fminbnd() to find the minimum value of that function and to find the maximum extreme use negative sign for the function and feed it to fminbnd().