How to save values changing in a loop without overwriting?

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Lauren Miller
Lauren Miller 2021-4-30
回答： Nagasai Bharat 2021-5-3
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
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Lauren Miller
Lauren Miller 2021-4-30
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
Rik 2021-4-30
Ran in:
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

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回答（1 个）

Nagasai Bharat
Nagasai Bharat 2021-5-3
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.

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