How do I get the matrix p

Question

LOKESH UDATHA 2019-3-17

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https://ww2.mathworks.cn/matlabcentral/answers/450602-how-do-i-get-the-matrix-p

评论： Walter Roberson 2019-3-18

Hello,

I am trying to solve the a matrix using solve function, not able to figure it out.

clear all
clc
syms x1 x2 M k L dx1 dx2 p
% Displacement of the bar
xg=(x1+x2)/2;
% Rotation of the bar
thi=(x2-x1)/L;
%moment of inertia
J=M*L^2/12;
dxg=(dx1+dx2)/2;
dthi=(dx2-dx1)/L;
% Kinetic energy
KE=0.5*((M*dxg^2)+(J*dthi^2));
% Potenial Engergy
PE=0.5*(2*k*x1^2+3*k*x2^2);
u=[x1 x2];
du=[dx1;dx2];
s=solve(KE==0.5.*transpose(du)*p*du);

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LOKESH UDATHA 2019-3-18

Thanks a lot, but a small problem

my p is a 2*2 matrix but I am getting sloution as a scalar.

Walter Roberson 2019-3-18

No it isn't . u is 1 x 2 so transpose of u is 2 x 1. You cannot do 2 x 1 * 2 x 2 * 1 x 2 because none of the inner dimensions match. Your u would have to be 2 x 1 to fix that .

There is not enough information to isolate 2 x 2 p.

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