Plotting help

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Alex 2011-9-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/16984-plotting-help

Hi, I'm pretty new to Matlab, and I tried to execute this script:

eq1 = '((((1.5-(x-(i*(y))))/(1.5+(x-(i*(y)))))+((((x-(i*y))-((3.46163-(i*(0)))))/((x-(i*(y)))+(3.46163-(i*(0)))))*(exp(-2*i*((pi*2)/1796)*(x-(i*(y)))*z))))/(1+(((1.5-(x-(i*(y))))/(1.5+(x-(i*(y)))))*(((x-(i*(y)))-(3.46163-(i*(0))))/((x-(i*(y)))+(3.46163-(i*(0)))))*(exp(-2*i*((pi*2)/1796)*(x-(i*(y)))*z)))))-.30441';
eq2 = '((((1.5-(x-(i*(y))))/(1.5+(x-(i*(y)))))+((((x-(i*y))-((3.46153-(i*(0)))))/((x-(i*(y)))+(3.46153-(i*(0)))))*(exp(-2*i*((pi*2)/1798)*(x-(i*(y)))*z))))/(1+(((1.5-(x-(i*(y))))/(1.5+(x-(i*(y)))))*(((x-(i*(y)))-(3.46153-(i*(0))))/((x-(i*(y)))+(3.46153-(i*(0)))))*(exp(-2*i*((pi*2)/1798)*(x-(i*(y)))*z)))))-.30440';
eq3 = '((((1.5-(x-(i*(y))))/(1.5+(x-(i*(y)))))+((((x-(i*y))-((3.46143-(i*(0)))))/((x-(i*(y)))+(3.46143-(i*(0)))))*(exp(-2*i*((pi*2)/1800)*(x-(i*(y)))*z))))/(1+(((1.5-(x-(i*(y))))/(1.5+(x-(i*(y)))))*(((x-(i*(y)))-(3.46143-(i*(0))))/((x-(i*(y)))+(3.46143-(i*(0)))))*(exp(-2*i*((pi*2)/1800)*(x-(i*(y)))*z)))))-.30439';
ezplot(eq1), hold on;
ezplot(eq2), hold on;
ezplot(eq3), hold off;

but it didn't work (some of you want to sternly tell me off right now, I know). Here is the error message:

??? Error using ==> char
Cell elements must be character arrays.
Error in ==> ezplot at 158
      fmsg = char(f);
Error in ==> nonlintest2 at 4
ezplot(eq1), hold on;
Error in ==> run at 74
    evalin('caller',[script ';']);

So, as a new user, I don't know how to use this error report very well, and looking online has gotten me some approximate info, but nothing that truly explains my situation to me. Can anyone help me with this please? I'd love to learn how to make this work.

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the cyclist 2011-9-28

Why did you enclose eq1, etc., in single quotes?

Fangjun Jiang 2011-9-28

@cyclist, to use ezplot()

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回答（1 个）

Walter Roberson 2011-9-28

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/16984-plotting-help#answer_22906

It is a bug in ezplot in constructing the error message to tell you that ezplot cannot be used to plot equations in more than 2 variables.

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Walter Roberson 2011-10-2

Those equations are difficult to solve, even individually by substituting values in to free variables.

Alex 2011-10-3

Yeah, that's the difficulty that I'm having with this. I don't know a lot about the language of Matlab, nor it's graphing capabilities, hence the post. If I had the optimization toolbox I could try using fsolve, but I don't, which leaves me in a pickle.

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