The following example from tccs/lowrank/impres shows a wave snapshot from a point source in an isotropic medium with a variable velocity.
sfisolr2 takes two inputs: the velocity model as standard input and the file given by fft= to specify the dimensions of the Fourier-transformed grid (the values in this file are not used). The program produces two outputs: the right decomposition matrix in the standard output, and the left decomposion matrix specified by left=. To make the results reproducible despite the randomization algorithm, set seed= for pseudorandom number generation.
The rank of the lowrank approximation is controlled by several parameters. The most important of those is the time step size dt=. The other controlling parameters are the approximation tolerance eps= and the number of random probes (maximum rank) npk=.
The related programs are sfanisolr2 for the anisotropic (TTI) case, and sfisolr3 for the 3-D case. The following example from tccs/lowrank/threed shows a 3-D wavefield snapshot computed with sfisolr3: