What am I doing wrong here? I am trying to recreate following highlighted equations in the table.

Question

Nissal Arachchige 2021-3-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/784831-what-am-i-doing-wrong-here-i-am-trying-to-recreate-following-highlighted-equations-in-the-table

评论： Paul Hoffrichter 2021-3-28

采纳的回答： Paul Hoffrichter

在 MATLAB Online 中打开

ep = linspace(0,1);
m1 = 1.5; m2 = 3.8;
ep0= 1; alpha = 0.785; epp = 0.11;
qep = (2.76*ep*cosh((3*ep)-1.92));
I1 = ep.^ m1;
I2 = ep.^ m2;
I3 = ep*((ep-epp)/(ep0-epp)).^alpha;
I6 = 1-(qep*((3*(1-ep))/(3-ep)));
Hold on
plot(ep,I1)
plot(ep,I2)
plot(ep,I3)
plot(ep,I6)
Hold off

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Answer 1

Paul Hoffrichter 2021-3-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/784831-what-am-i-doing-wrong-here-i-am-trying-to-recreate-following-highlighted-equations-in-the-table#answer_659596

编辑：Paul Hoffrichter 2021-3-27

在 MATLAB Online 中打开

clc; clear; clf
ep = linspace(0,1);
m1 = 1.5; m2 = 3.8;
ep0= 1; alpha = 0.785; epp = 0.11;
qep = (2.76*ep.*cosh((3*ep)-1.92));
I1 = ep.^ m1;
I2 = ep.^ m2;
zz = (ep-epp)/(ep0-epp);
zza = zz .^ alpha; % zza is complex
I3 = ep .* zza;
I6 = 1-(qep*((3*(1-ep))/(3-ep)));
hold on
plot(ep,I1);
plot(ep,I2)
plot(ep,I3) % This is Line 18 - usually do not plot a complex vector like this
plot(ep,I6)
hold off

warning:

Warning: Imaginary parts of complex X and/or Y arguments ignored. 
> In Untitled (line 18) 

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Nissal Arachchige 2021-3-27

No not at all. I was actually able to recognize my coading problem before you posted the answer and I got the same solution as you and the warning as well. I do not know why it does that. And I was supposed to recreate the follwing graph but ignore the points and the legend. I'm waiting for the feedback from my professor. I'll let you know if something intresting come up. Thanks again.

Paul Hoffrichter 2021-3-28

I was a surprised at first about the complex numbers. But then I thought about what if alpha was 0.5 instead of 0.785. Then if x is a negative number, we have a purely imaginary result for x^(.5)=sqrt(x)= sqrt{(-1) * abs(x)} = 0 + j*sqrt(abs(x)). For other values of alpha between (0.5, 1.0), we get complex numbers.