problem in finding inverse

Question

rakesh kumar 2023-12-20

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2062377-problem-in-finding-inverse

评论： Image Analyst 2023-12-20

在 MATLAB Online 中打开

%function[el5,f0]=data_cholesky(sigma,nel,l)

clc

clear all

sigma=0.15;

l=300;

nel=200; % number of elements

nnel=2; % number of nodes per element

ndof=1; % number of dofs per node

nnode=(nnel-1)*nel+1; % total number of nodes in system

sdof=nnode*ndof; % total system dofs

index=zeros(nnel*ndof,1);

mm=zeros(sdof, sdof);

bcdof(1)=1; % first dof (deflection at left end) is constrained

bcval(1)=0; % whose described value is 0

bcdof(2)=2; % 12th dof (slope at the symmetric end) is constrained

bcval(2)=0; % whose described value is 0

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

T = zeros(nel+1, 1); % Replace with your initial guess for x

i=1; %boundary condition

T(i) = 300;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

keq=zeros(nel+1,nel+1,l);

keq1=zeros(nel+1,1,l);

keq2=zeros(nel+1,nel,l);

keq3=zeros(nel,nel,l);

A1 =zeros(nel+1,1,l);

A2 =zeros(nel,1,l);

el40 = zeros(nel, l); % Initialize el4 as a 2D matrix

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

a=nel;

i=1:a;

b0=11;

mean0=zeros(3,b0);

vari0=zeros(3,b0);

kk(:,:,:)=zeros(sdof, sdof,l);

ss(:,:)=zeros(sdof, sdof);

m=zeros(2,2,l);

s=zeros(2,1,l);

k0 = zeros(2,1,l);

el0=zeros(nel,b0,l);

%for b0=1:b0

b=b0-1;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

ka = 200 ; % conductivity

tleng=50*10^-3; % total length

d =1*10^-3;

le=tleng/(nel);

k0 = (ka/le)*[1 -1;-1 1];%

P =3.14*d ; % perimeter;

h = 20; % convective heat transfer

Ac = 3.14*d^2/4; % cross area crosssection

q0 = 0;

m = (P * h * le) / (6 * Ac) * [2 1; 1 2];%

Tinf=30;

s = (q0 + (P*h/Ac)*Tinf)*[le*0.5;le*0.5]; %

s=diag(s);

s = repmat(s, [1, 1, l]);

m = repmat(m, [1, 1, l]);

%k0=repmat(k0, [1, 1, l]);

Q=zeros(nel+1,1);

Q(1)=1;

Q(nel+1)=0;

for iel=1:nel % loop for the total number of elements

edof = nnel*ndof;

start = (iel-1)*(nnel-1)*ndof;

%

for i=1:edof

index(i)=start+i;

end

edof = length (index);

for i=1:edof

ii=index(i) ;

for j=1:edof

jj=index(j) ;

mm(ii,jj)=mm(ii,jj)+m(i,j,l);

ss(ii,jj)=ss(ii,jj)+s(i,j,l);

end

for l=1:l

d1=tleng/nel;

d=1;

i=1:nel;

j=1:nel;

ee=zeros(nel,nel);

R=zeros(nel,nel);

e(i)=tleng/2*nel+(tleng/nel)*(i-1);

for i=1:nel

for j=1:nel

ee(i,j)=e(i)-e(j);

R(i,j)=sigma^2*exp(-abs(ee(i,j)/d));

end

C1=chol(R,'lower');

Z1=randn(nel,1);

alpha=C1*(Z1);

E0=1;

el4= ((1+alpha));

el40(:, l)= el4;

el=el4(1:nel);

el2= 1 + zeros( 1, 100 );

el3=[0.90991 0.98608 0.90314 1.1458 1.0554 0.91364 1.3918 0.61164 0.74829 1.369];

el5=E0*ones(1,20);

for iel=1:nel % loop for the total number of elements

edof = nnel*ndof;

start = (iel-1)*(nnel-1)*ndof;

%

for i=1:edof

index(i)=start+i;

end

c0(iel)=el4(iel);

k(:,:,iel)=c0(iel)*k0;

edof = length (index);

for i=1:edof

ii=index(i) ;

for j=1:edof

jj=index(j) ;

kk(ii,jj,l)=kk(ii,jj,l)+k(i,j,iel);

end

sss=diag(ss);

keq=kk+mm;

keq1=T(1)*keq(:,1);

keq2 =keq(:,2:end,:);

keq3=keq2(2:end,:,:);

A1(:,:,l)=sss+Q-keq1;

A2(:,:,l)=A1(2:end,:,l);

%A3(:,:,l)=inv(keq3(:,:,l));

%temp(:,:,l)=A3(:,:,l)*A2(:,:,l);

temp(:,:,l)=keq3(:,:,l)\A2(:,:,l);

end

% Define the length and number of elements

temp1=squeeze(temp);

T0 =300 * ones(1,l);

temp1=[T0;temp1];

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%temp1([2:4],:)=[]

x= linspace(0,tleng,nel+1);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%55

x=x';

for i=1:l

plot(x,temp1(:,i))

hold on

end

mean_temp =mean(temp1,2) ;

mean_temp(1:3)

ans = 3×1

300.0000 341.6619 340.4453

the variation of temp vs x should be continously dectreasing. but when i run it several times .sometimes temp increses with x please help

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Image Analyst 2023-12-20

在 MATLAB Online 中打开

I have no idea what this weakly commented code does. Try adding more comments to explain the various things. Your subject says "problem in finding inverse" so I guess you want to find the inverse of a matrix. About all I can say is that if you want the inverse of a matrix, try inv

help inv
 INV    Matrix inverse.
    INV(X) is the inverse of the square matrix X.
    A warning message is printed if X is badly scaled or
    nearly singular.
 
    See also PINV, COND, CONDEST, LSQMINNORM, LSQNONNEG, LSCOV.

    Documentation for inv
       doc inv

    Other uses of inv

       codistributed/inv    InputOutputModel/inv    sym/inv
       gpuArray/inv         quantumCircuit/inv      symbolic/inv

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