Error using surf X,Y, Z and C cannot be complex

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vetri veeran 2017-3-25

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评论： Jan 2017-3-25

采纳的回答： Jan

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Hi all,

I want to draw 3D plot using surf command for vt = 0, -0.1...-0.5

I am getting an error as,

Error using surf X,Y, Z and C cannot be complex

My code is given below,

B = 1e-4; sigma_on = 0.45; x_on = 0.06; sigma_p = 4e-5; A = 1e-10; sigma_off = 0.013; x_off = 0.4; G_m = 0.025; rho = 1e-3; v_m = -0.5;

vt= 0:0.1:0.5;

t = 0.01:0.01:1;

for v = 1:length(vt)

    v_m = -vt(v);
    for x = 1:length(t)
        G(x) = G_m*t(x)+ exp(sqrt(v_m));
        f1(x) = A*sinh(v_m/sigma_off)*exp(-(x_off^2/t(x)^2));
        f2(x) = B*sinh(v_m/sigma_on)*exp(-(t(x)^2/x_on^2));
        f(x) = f1(x) + f2(x);
        final(v,x)=log(f(x));
    end

end;

surf(t,vt,final);

Can anyone help me.

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Answer 1

Jan 2017-3-25

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编辑：Steven Lord 2017-3-25

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The error message is clear: "X,Y, Z and C cannot be complex". Obviously there are complex values. All we see is the failing code, but we cannot guess reliably, what its intention is. Therefore it is hard (or random) to suggest an improvement.

Maybe you want:

surf(t, vt, real(final));

or

surf(t, vt, abs(final));

or your calculations are wrong.

[SL: fixed typo in last code segment.]

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Jan 2017-3-25

Thanks, Steven.

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Answer 2

Star Strider 2017-3-25

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The logarithm of a negative number will be complex. There are several ways to avoid that, the easiest being:

final(v,x)=log(abs(f(x)));

Note that the logarithm of 0 is -Inf, so you may want to trap ‘f(x)’ to prevent it from being zero as well. The easiest way to do that would be to have it equal NaN if it is zero, because NaN values will not plot. Consider setting the negative values of ‘f(x)’ to NaN as well, as one option.