Why is my code producing a 0's at the 11th Column

Question

William david 2023-7-27

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回答： C B 2023-7-27

All of a sudden the 11th column of p is falling to zero and stays that way for the rest of the columns following it. I see no reason for this as the variables used to compute p do not change randomly.

clear all; clc; close all;

tic;

z1 = 1;

z1 = 2;

z2 = 2*z1;

z = [z1,z2];

la1 = 1/3;

la2 = 1/3;

la = [la1,la2];

z_ave = (z1*la2 + z2*la1)/(la1 + la2);

sigma = 0.75;

theta = sigma/(sigma-1);

pe = 1.68;

xi = 0.01:0.01:0.2;

pe = linspace(1,1.5,100);

p = zeros(length(xi),length(pe))

for i = 1:20

for j = 1:10

p(i,j) = (1+xi(i)*pe(j)^theta)^(1/theta)

end

plot(pe,p(1,:))

I expect the values to stay around 0.94 and lower, but there seems to be a problem.

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Answer 1

Star Strider 2023-7-27

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Could it be because that is how you defined it?

xi = 0.01:0.01:0.2;

pe = linspace(1,1.5,100);

p = zeros(length(xi),length(pe))

It seems that ‘p’ is preallocated as a (30x100) matrix of zeros (preallocation is good programming practice), and you are onlly writing tto the first 20 rows and the first 10 columns of it.

.

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Answer 2

C B 2023-7-27

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Looking at pe(j), i think your J loop should run for length of pe, is this what you are expecting?

z1 = 1;

z1 = 2;

z2 = 2*z1;

z = [z1,z2];

la1 = 1/3;

la2 = 1/3;

la = [la1,la2];

z_ave = (z1*la2 + z2*la1)/(la1 + la2);

sigma = 0.75;

theta = sigma/(sigma-1);

pe = 1.68;

xi = 0.01:0.01:0.2;

pe = linspace(1,1.5,100)

pe = 1×100

1.0000 1.0051 1.0101 1.0152 1.0202 1.0253 1.0303 1.0354 1.0404 1.0455 1.0505 1.0556 1.0606 1.0657 1.0707 1.0758 1.0808 1.0859 1.0909 1.0960 1.1010 1.1061 1.1111 1.1162 1.1212 1.1263 1.1313 1.1364 1.1414 1.1465

p = zeros(length(xi),length(pe));

length(pe)

ans = 100

for i = 1:length(xi)

for j = 1:length(pe)

p(i,j) = (1+xi(i)*pe(j)^theta)^(1/theta);

end

plot(pe,p(1,:))