Questions tagged [complex]

Questions about using complex numbers in Mathematica. This includes basic arithmetic, functions of complex numbers, plotting complex functions, and dealing with branch cuts.

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6
votes
1answer
105 views

Why ArcTan[1, 0. I ] yields -1.5708+0. I?

Why ArcTan[1, 0. I ] yields -1.5708+0. I ? The result should equal to 0. Is this a bug?
0
votes
2answers
30 views

expression containing radicals of imaginary numbers

I can't bear an expression containing radicals of imaginary numbers, in case it can be expressed as in terms of radicals of real numbers only. For example, I can't bear the expression Sqrt[2 + i] ...
5
votes
1answer
112 views

Visualizing Riemann surface (two branches) of logarithm

I'm trying to plot two branches of the complex multi-valued function: (In a previous post - linked above-, Mathematica found the branch cut of the following function between -1 and 0) $1-z\ln[(1+z)/z]...
4
votes
2answers
145 views

To plot branch cut of logarithm

I like to see the branch cut of the function: $$1 - z \ln[(1+z)/z].$$ If I plot it in the complex plane: ...
1
vote
1answer
58 views

How to plot special contour lines for a “Ridge System” of complex function?

Mathematica makes it very easy to to plot the contour lines for a function of two real variables using ContourPlot. It also makes it very easy to plot the ...
0
votes
0answers
55 views

Unexpected difference between integral and summation?

I am trying to integrating something like: Integrate[Exp[-i*(k*x+k*z)]*Exp[-(x^2+z^2)],{x,-largenumber,largenumber},{z,-largenumber,largenumber}] My issue is that ...
2
votes
2answers
153 views

Getting an Accurate Transformed Region (Part II)

I asked earlier about transforming a set of curves and getting an accurate plot when a curve goes to infinity: Getting an Accurate Transformed Region Here is an example where a transformed region ...
1
vote
1answer
100 views

Getting an Accurate Transformed Region

I would like to get an accurate plot of the image of concentric circles under the transformation $$f(z) = \log(1+z).$$ I've defined $\cal R$ as the union of a few circles: ...
1
vote
1answer
71 views

How to extract only real part of 2nd root solution to C code?

I have this cubic polynomial: ...
3
votes
1answer
167 views

How to solve PDE with periodic and anti-periodic b.c.?

I need to solve the PDE for a complex function $A(x,t)=A_r(x,t)+iA_i(x,t)$ ...
0
votes
0answers
34 views

Why do all the Roots not show up in ContourPlot of an equation?

Roots by Normal Method: f[x_] := (Sin[x] + Cos[x] - Sqrt[2]) Sqrt[-11 x - x^2 - 30]; Reduce[(Sin[x] + Cos[x] - Sqrt[2]) Sqrt[-11 x - x^2 - 30] == 0, x] Which ...
1
vote
1answer
57 views

Verification of ComplexPlot

from Wegert Visual complex functions. I am trying to verify a phase portrait by reproducing it with Mathematica. The only problem is that I am misunderstanding the ...
0
votes
0answers
15 views

Set conditions on SingularValueDecomposition

I'm a new user of Mathematica, and I am having some issues with SingularValueDecomposition. This function returns three matrices {u,v,w}, with v that is diagonal and u,w unitary such that u.v....
0
votes
1answer
36 views

Conditions to make unitary a given matrix

Suppose I have some symmetric matrix W = {{c[1, 1], c[1, 2], c[1, 3]}, {c[1, 2], c[2, 2],c[2, 3]}, {c[1, 3], c[2, 3], c[3, 3]}}; where the c's are complex and I ...
0
votes
1answer
36 views

Interesting output in Integrate [closed]

I found interesting behaviour, best illustrated in the following example. When trying to evaluate Integrate[1/(d^2 - 1), d] Mathematica 11.3 gives the following ...
1
vote
1answer
80 views

Sharp jagged lines in Plot3D

I have the following function of five parameters of which I would like to construct a 3D density plot using Plot3D ...
1
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2answers
35 views

Different styles for different points in ComplexListPlot?

I'd like to use ComplexListPlot to show a point and its image under a complex function, with the point and image having different styles, say different colors. Use,...
2
votes
1answer
46 views

Plotting Complex Numbers as “Arrows” on the Complex Plane

Given the following complex numbers (defined as the values of two functions f and g defined only on the points ...
2
votes
1answer
85 views

Taking real and imaginary parts after reciprocal

I noticed the following strange scenario. When I defined a variable to be real, Mathematica does not only recognize that it is real after taking an inverse. How can I resolve this so that it will ...
0
votes
1answer
52 views

Adding degrees to complex numbers

I'd like to take the complex number $(1 + 0i)$ and (i) multiply it by $0.5$ and (ii) add 45 degrees to it (without changing its magnitude). But I'd like to get its complex represenation in non-polar ...
0
votes
1answer
56 views

Showing a specific (complex) point in a Graphic [closed]

Somewhat related to a previous post that I made - Complex infinity at a point and division by zero I'm still following the book on this example and I've come to the part where one draws the '...
2
votes
1answer
45 views

Discolored ComplexPlot ColorFunction [closed]

I have this code. ...
0
votes
1answer
48 views

Complex infinity at a point and division by zero

Edit: I've found out that the book was written for Mathematica 7, which was a pretty long time ago. It boils down to changes in syntax most probably, but simple renaming to lower lettercase does not ...
0
votes
0answers
25 views

Expanding the complex conjugate of a Mathieu function as a series

In my calculations, I found this equation: ...
0
votes
1answer
37 views

Can we make a labelled parametric plot in which the parameter is integer? [closed]

Can we make a labelled parametric plot in which the parameters are integers? I'm just using Wolfram Alpha but could equally use Mathematica Online, and want something like here. I want to plot ...
1
vote
0answers
69 views

How can I get Mathematica to recognize that $ab^* + ba^* = 2\Re(ab^*)$?

Mathematica understands that $z + z^* = 2\Re(z)$, FullSimply[z + Conjugate[z]] (* output: 2 Re[z] *) However, Mathematica does not simplify the expression ...
0
votes
1answer
40 views

Complex Exponentials to Trig Functions?

I have an expression expr = 1/2 a E^(-3 I ω t) (E^(3 I ω t)+2 Cos[π x/a]) (1+2 E^(3 I ω t) Cos[π x/a]) Sin[π x/a]^2; expr // TeXForm $\frac{1}{2} a e^{-3 i t \...
2
votes
2answers
121 views

How to show that $f(z) = z^2 + 1$ intersects the line through the roots of $f(z) = 0$ in ComplexPlot3D?

I have plotted the complex function $f(z) = z^2+1$ by using the following code: ComplexPlot3D[z^2+1, {z, -5 - 5 I, 5 + 5 I}] However, I want to show that $z^2+1$ intersects the line $\Re(z) = 0$. ...
0
votes
1answer
86 views

How to plot the complex function $f(z) = z^2 + 1$ in a three-dimensional plot with colouring?

I've noticed that there are different ways to plot a complex function. What I am interested in, is a three-dimensional plot with colouring of the complex function $f(z) = z^2 + 1$. Here is an example ...
3
votes
1answer
211 views

Using Im[] and Re[] Correctly

Hi I just want to check my code is working properly as I am trying to rule out any errors. I'm integrating 4 coupled ODE's that have real and imaginary terms, so I have 8 equations. The section of ...
0
votes
1answer
49 views

Finding the negative real root of in set of solutions under a varying constraint

Suppose I have a function and its derivative like: V = x^3.5 - x*y Vx = D[V, x] I first solve V for ...
3
votes
1answer
122 views

Finding the maximum real part of roots

Suppose that I have this problem ...
1
vote
1answer
71 views

Plotting $f: x + i\,y \mapsto u + i\, v$ with Plot3D and mapping $v$ to color

Mathematica already has ComplexPlot3D that plots ReIm[x, y] against Abs[f(z)] and ...
2
votes
2answers
631 views

Weird result in complex limit

I am trying to evaluate a limit: gamma[w_] = Sqrt[-(u*e)w^2 + I*(u*s)w]; Limit[Re[gamma[x]], {x -> DirectedInfinity[1]}] I calculated the limit by hand, and ...
0
votes
0answers
82 views

Plot the maximum of the real parts of the eigenvalues of a trancendental equation

Basically I have this matrix ...
10
votes
2answers
817 views

Why does Arg'[1. + I] return -0.5?

From the document we know that Arg[z] gives the gives the argument of the complex number z. Then how about ...
-1
votes
1answer
105 views

ComplexPlot3D and essential singularities [closed]

I am trying to understand the behavior of the functions $$ f(z) = e^\frac{1}{z} \qquad \text{and} \qquad \frac{1}{f(z)} = \frac{1}{e^\frac{1}{z}} $$ in the neighborhood of $z=0$. From the power ...
1
vote
0answers
30 views

Discontinuities in taking the roots of a complex function

I have the following functions e1, e2, and e3 which consists of the functions ...
0
votes
0answers
24 views

Integrating System of ODE's

I'm trying to integrate the system $$\frac{d}{d z} \left[ \begin{array}{l}{\hat{a}} \\ {\hat{b}}\end{array}\right]=\frac{i \omega}{\overline{c}} \left[ \begin{array}{cc}{\left(\Delta_{l}^{(+)}-1\...
1
vote
0answers
58 views

Efficient evaluation of real/imaginary parts of long expressions

I have the following, rather compact, but complex, expression (see below). I simply want the real part of this. Now, when I do the usual, i.e., ...
0
votes
2answers
80 views

Result with assumptions contradicts previous result

Without assuming anything on the argument of the complex number inside the Gamma function ...
1
vote
1answer
33 views

Mathematica is not simplifying trignometric functions under Abs although I provide assumptions

I am trying to simplify a simple expression, (1/2)*((-Pi)*Abs[Sin[t]] - Pi*Abs[Sin[t - 2*Pi]] - 2*Pi*Abs[Sin[t - Pi]] + 4) i.e $$ \frac{1}{2} (-2 \pi \...
1
vote
2answers
74 views

Taking absolute value of complex variable

I'm trying to take absolute value squared of certain objects. Say I have y=alpha and I know that |alpha|^2 = alpha*Conjugate[alpha]. How do I take Abs[y]^2 ...
1
vote
1answer
89 views

How to define a complex function with assumptions?

I'm trying to define a complex function to be able to do analytic calculations. Specifically, I want to define a function $A(x,t)$ in the complex plane with argument $\theta(x,t)$ and modulus $R(x,t)&...
12
votes
3answers
420 views

Finding and visualization of branch cuts and branch points

Is it possible to determine branch cuts and branch points for complicated functions using mathematica Iam trying to determine the brnach cuts and branch points of this complicated function We have ...
1
vote
1answer
62 views

Find roots of transcendental function in regional complex plane

I want to know how many roots does the following equation have and how to solve them all. $f(z)=\frac{\text{sech}(35.0937 x)}{\left(e^{70.1873 x}-1.\right) x} \left((0.\, +0.0235822 i) x^2 \exp \...
1
vote
3answers
77 views

How to take a derivative of a function with a real part taken

Consider f[x_]=Re[x^3] I now take the derivative of this D[f[x],x] and the result is ...
4
votes
4answers
196 views

How to find image of a complex function with given constraints?

I am very new to Mathematica. I have started learning it only last month. I would like to graph the image of some complex valued polynomials with some provided conditions. For example: $$ p(z_1,z_2,...
1
vote
1answer
105 views

Mathematica doesn't extract Re and Im parts properly

I have a code: ...
0
votes
1answer
81 views

Complex number as the result of an integral [closed]

My question has been asked before by other members, however, I didn't find the answer to their question helpful in my case. I'm doing a simple numerical integral with real numbers in mathematica, but ...