plot different curves(different output of a for loops) in single graph

hi ive made a code to solve a set linear equation

also the reside r i.e r= (rhs-lhs)/rhs

so i need to find r of every loop while finding the root(x) value.

this different r1 r2 r3 r4 r5 have to plotted on same graph with different colours.

kindly guide me how to plot different r in single curve of this code.

A=[2 1 1 1 1; 1 3 1 2 1; 1 2 5 1 3; 2 3 1 4 1; 2 1 1 2 3]; %given matrix
b=[5 1 17 0 10]';
r=[100 100 100 100 100]';
Em= 0.002; %input("max error permissible"); %get max error permissible
z=100;% input("number of iterations");
%gauss  method for linear equation
for i=1:size(A,1) %get input intial guess of x from user
    switch i
        case 1
            x(i)=input("guess x1");
        case 2
            x(i)=input("guess x2");
        case 3
            x(i)=input("guess x3");
        case 4
            x(i)=input("guess x4");
        case 5
            x(i)=input("guess x5");
    end
end
E=100 ; %keeping intial error as 100%
iter=0; %keep iteration count as 0
plotG=[];
z=[];
while E>Em
    xold=x; %keeping old value
    for i= 1:size(A,1)
        sum=0; %intialise sum=0
        sum1=0; %intialise sum1=0 for using in finding r(i) i.e (RHS-LHS)/RHS
        for j=1:i-1
            sum=sum+A(i,j)*x(j);
        end
        for j=i+1:size(A,1)
            sum=sum+A(i,j)*xold(j);
        end
        x(i)=(1/A(i,i))*(b(i)-sum); %updation using seidal method
        if i==4
            r(i)=(b(i)-sum-(sum1+A(i,i)*x(i)));
        else
            r(i)=(1/b(i))*(b(i)-sum-(sum1+A(i,i)*x(i)));
            
        end
        iter=iter+1; %keep count of iteration
        z=r(i);
        %y(iter,:)=x; %keep check on the output value of x after each iteration
        
        E=abs(((xold-x)/x)*100); %compute the error percentage for convergence criteria
        plotG=[plotG;z];
        r
        plot(1:iter,plotG)
        hold on
    end
end
disp("converged value of x1 to x5 is");
x

Answer 1

[Milan Bansal]

Hi,

I understand that you are trying to plot different plots for "r" on the same plot in different colours while using the "for" loop.

iter=iter+1; %keep count of iteration 
z=r(i); 
%y(iter,:)=x; %keep check on the output value of x after each iteration 

E=abs(((xold-x)/x)*100); %compute the error percentage for convergence criteria 
plotG=[plotG;z]; 
r 
plot(1:iter,plotG) 
hold on 

In the above part of the your code, value of "iter" is incremented and a new element "z" is concatenated with "plotG" array in each iteration of the "for" loop. Then, a "line" plot is plotted for "plotG" array. This is resulting is overlapping of the same curve with a new point in each iteration, hence new curves are not visible in different colors.

Instead of using "plot" function, you may use "scatter" function to plot values of r in different colors for each interation in "for" loop. Try using the code given below.

iter=iter+1; %keep count of iteration 
z=r(i); 
%y(iter,:)=x; %keep check on the output value of x after each iteration 

E=abs(((xold-x)/x)*100); %compute the error percentage for convergence criteria 
plotG=[plotG;z]; 
r 
scatter(iter,plotG(iter)) 
hold on 

Refer to the below documentation link to learn more about "scatter" plot.

https://www.mathworks.com/help/matlab/ref/scatter.html?searchHighlight=scatter&s_tid=srchtitle_support_results_1_scatter