How to save values changing in a loop without overwriting?

I need every 100th value for

emag

to be saved against the corresponding value of t so that I can plot the results, however I have tried

        dlmwrite('filename.txt', emag,'-append', '\t')
        dlmwrite('filename.txt', t,'-append', '\t')

and it's not working for me and I'm not very well versed with MATLAB at all so any help would be very greatly appreciated. This is my loop;

    m = 0;
for i = 1: m
    m = m + 1;
    if m == 100
        C{i} = emag;
        C2{i} = t;
        E(i,1) = emag;
        E(i,2) = t;
        %m = 0;
t = t + steps*delta;
    end   
end

[Rik]

Your loop will not run, because 1:0 returns an empty array.

[Lauren Miller]

Hiya, it's giving all the right values in the command window!

[Rik]

This code will not print anything to the command window, unless emag, steps, or delta is a function.

[Lauren Miller]

It definitely is printing values to the command window,

The whole block of code is

D=dot(P(2,:), V(2,:))
e1=norm(V(2,:));
e1=e1^2
mu=G*M(1)
e2=e1/mu
r1=norm(P(2,:))
e3=e2/r1
e4=e3*P(2,:)
e5=D/mu
e6=e5*V(2,:)
e=e4-e6
emag=norm(e)
emag=emag/1.0e+10
%t = t + steps*delta;
steps = 100;
delta = 0.5;
update_plot(P,H,t)
    m = 0;
for i = 1: m
    m = m + 1;
    if m == 100
        C{i} = emag;
                    C2{i} = t;
                    E(i,1) = emag;
                    E(i,2) = t;
                    matrixToWrite = [t emag];
                    writematrix(matrixToWrite, 'myData.txt')
        %m = 0;
            t = t + steps*delta;

[Rik]

The loop isn't, the code before it is.

%generate values to avoid errors
P=rand(2,20);V=rand(2,20);G=rand;M=rand;H=rand;t=rand;

D=dot(P(2,:), V(2,:))

D = 4.1719

e1=norm(V(2,:));
e1=e1^2

e1 = 5.6835

mu=G*M(1)

mu = 0.5082

e2=e1/mu

e2 = 11.1826

r1=norm(P(2,:))

r1 = 2.7853

e3=e2/r1

e3 = 4.0148

e4=e3*P(2,:)

e4 = 1×20

1.2742 2.4955 3.5995 3.0196 2.2990 0.7363 3.3123 0.1011 2.8078 1.7513 3.4836 3.5537 1.2469 3.0465 3.8202 1.7159 0.5303 1.6641 3.1727 1.0536

e5=D/mu

e5 = 8.2083

e6=e5*V(2,:)

e6 = 1×20

3.9968 0.9303 7.7538 0.9089 1.7754 7.5097 4.9340 5.2943 1.7248 5.1817 0.4586 4.4645 3.1174 4.0714 1.0209 2.6601 7.5543 1.4035 0.9719 6.9904

e=e4-e6

e = 1×20

-2.7226 1.5652 -4.1542 2.1106 0.5236 -6.7734 -1.6217 -5.1932 1.0829 -3.4304 3.0250 -0.9108 -1.8706 -1.0249 2.7993 -0.9442 -7.0240 0.2607 2.2008 -5.9368

emag=norm(e)

emag = 15.2649

emag=emag/1.0e+10

emag = 1.5265e-09

%t = t + steps*delta;
steps = 100;
delta = 0.5;
update_plot(P,H,t)
    m = 0;
for i = 1: m
    m = m + 1;
    if m == 100
        C{i} = emag;
                    C2{i} = t;
                    E(i,1) = emag;
                    E(i,2) = t;
                    matrixToWrite = [t emag];
                    writematrix(matrixToWrite, 'myData.txt')
        %m = 0;
            t = t + steps*delta;
    end
end
function update_plot(P,H,t)
end

Answer 1

[Nagasai Bharat]

Hi,

From my understanding you are trying to loop over and save every 100th element corresponding to 100th element is t.

The problem arising in the initialization of the for loop . In you code, the statements inside the loop are not excecuted due to incorrect use of for.

for i = a:b

Here while indexing an array i has to be an whole number and also b should be greater than a for the looping. There variables a and b should be already defined and not be changed. Other alternatives to use is the while loop as there a logical condition would be checked to loop further.