sfisolr2 performs low-rank decomposition for wave propagation in a 2-D isotropic medium using lowrank approximation method.

The output of sfisolr2 can be used by other programs, such as sffftwave2 or sffftexp0 to perform wave modeling or reverse-time migration.

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:

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