Problem with abs()

Question

Patrick Philipiak 2017-10-25

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/363152-problem-with-abs

编辑： Patrick Philipiak 2017-10-25

AuswertungFeldDirektvonHand.m

So i have a function which i plot that looks like this

 f(x)= (1i*omega*mueh)*(2*d^3/3*1000/(pi*120))*(-(i *(x - x1)* exp(-i* k* sqrt((x - x1)^2 + (y - y1)^2 + (z - z1)^2))* (k* sqrt((x - x1)^2 + (y - y1)^2 + (z - z1)^2) - i))/(4* pi *((x - x1)^2 + (y - y1)^2 + (z - z1)^2)^(3/2)))

It is a function for an the z component of an electric field. I now need the absolut value of that field. Here comes the kicker.

I get two different results. Its different between abs() and doing sqrt(a^2+b^2). So it seems like i dont really know enough about abs() or what it really does. I though i should get the same result. can someone enlighten me so i dont fall for this again?

I Attached my script. There is a lot going on. Its basicly a superpositon of the values.

The important lines are 136 and 138