Natural logarithm: 3D plots over the complex plane

Log

$Mathematica Notation$

Elementary Functions

Log[z]

Visualizations

3D plots over the complex plane

Entering the complex plane

Upper picture: in the upper half of the near the real axis viewed from the lower half‐plane. Lower picture: in the lower half of the near the real axis viewed from the upper half‐plane. Here the complex variable is expressed as . The red surface is the real part of . The blue, semi‐transparent surface is the imaginary part of . The pink tube is the real part of the function along the real axis and the skyblue tube is the imaginary part of the function along the real axis. At , the function has a logarithmic singularity. Along the real axis, the real part of approaches as . Along the real axis, the imaginary part of is piecewise constant; going away from the real axis into the gives a function that approaches . The imaginary part is discontinuous along the interval . The imaginary part has upper lip continuity.

Branch cuts

The real part and the imaginary part of over the . The left graphic shows and the right graphic shows . Along the interval the function has a branch cut. The imaginary part has discontinuities along the branch cut. At , the function has a logarithmic branch point. The viewpoint is from the lower half‐plane.

The real part and the imaginary part of over the . The left graphic shows and the right graphic shows . The viewpoint is from the upper half‐plane.

The branch cuts of the real part and the imaginary part of over the . The left graphic shows and the right graphic shows . The red and blue vertical surfaces connect points from the immediate lower and upper neighborhoods of the branch cuts. The branch point at is a logarithmic branch point. Only the imaginary part shows discontinuities due to the branch cut. The viewpoint is from the lower half‐plane.

The branch cuts of the real part and the imaginary part of over the . The left graphic shows and the right graphic shows . The red and blue vertical surfaces connect points from the immediate lower and upper neighborhood of the branch cuts. The viewpoint is from the upper half‐plane.

Real part over the complex plane

The real part of where . The surface is colored according to the imaginary part. The right graphic is a contour plot of the scaled real part, meaning the height values of the left graphic translate into color values in the right graphic. Red is smallest and violet is largest. The function has a logarithmic singularity at ; going away from the real axis into the upper half of the gives a function that asymptotically approaches ∞.

The absolute value of the real part of where . The surface is colored according to the absolute value of the imaginary part. The right graphic is a contour plot of the scaled absolute value of the real part , meaning the height values of the left graphic translate into color values in the right graphic. Red is smallest and violet is largest. The function has a logarithmic singularity at ; going away from the real axis into the upper half of the gives a function that asymptotically approaches ∞.

Imaginary part over the complex plane

The imaginary part of where . The surface is colored according to the real part. The right graphic is a contour plot of the scaled imaginary part, meaning the height values of the left graphic translate into color values in the right graphic. Red is smallest and violet is largest. Along the real axis the imaginary part of vanishes identically for ; going away from the real axis into the gives a function that approaches . is a discontinuous function over the . The branch point at is a logarithmic branch point.

The absolute value of the imaginary part of where . The surface is colored according to the absolute value of the real part. The right graphic is a contour plot of the scaled absolute value of the imaginary part, meaning the height values of the left graphic translate into color values in the right graphic. Red is smallest and violet is largest. Along the real axis the imaginary part of vanishes identically for ; going away from the real axis into the gives a function that approaches . is a discontinuous function over the . The branch point at is a logarithmic branch point.

Absolute value part over the complex plane

The absolute value of where . The surface is colored according to the argument. The right graphic is a contour plot of the scaled absolute value, meaning the height values of the left graphic translate into color values in the right graphic. Red is smallest and violet is largest.

Argument over the complex plane

The argument of where . The surface is colored according to the absolute value. The right graphic is a contour plot of the scaled argument, meaning the height values of the left graphic translate into color values in the right graphic. Red is smallest and violet is largest. has lines of discontinuities over the .

The square of the sine of the argument of where . For dominantly real values, the function values are near 0, and for dominantly imaginary values, the function values are near 1. The surface is colored according to the absolute value. The right graphic is a cyclically colored contour plot of the argument. Red represents arguments near and light‐blue represents arguments near 0.

Zero-pole plot

The logarithm of the absolute value of where in the upper half‐plane. The surface is colored according to the square of the argument. In this plot, zeros are easily visible as spikes extending downwards and poles and logarithmic singularities as spikes extending upwards. The logarithmic branch point at and the zero at are visible.

Real part over the complex plane near infinity

Imaginary part over the complex plane near infinity

Absolute value part over the complex plane near infinity

Argument over the complex plane near infinity

The square of the sine of the argument of where . For dominantly real values, the functions values are near 0, and for dominantly imaginary values, the function values are near 1. The surface is colored according to the absolute value. The right graphic is a cyclically colored contour plot of the argument. Red represents arguments near and light‐blue represents arguments near 0.

Zero-pole plot near infinity

Log[a,z]