# focus

Create input signal based on source mask and focus position.

## Syntax

    input_signal_mat = focus(kgrid, input_signal, source_mask, focus_position, sound_speed)

## Description

`focus` takes a single input signal and a source mask and creates an input signal matrix (with one input signal for each source point). The appropriate time delays required to focus the signals at a given position in Cartesian space are automatically added based on the user inputs for `focus_position` and `sound_speed`.

## Inputs

`kgrid` | k-Wave grid object returned by `kWaveGrid`
`input_signal` | single time series input
`source_mask` | matrix specifying the positions of the time varying source distribution (i.e., source.p_mask or source.u_mask)
`focus_position` | position of the focus in Cartesian coordinates
`sound_speed` | scalar sound speed

## Outputs

`input_signal_mat` | matrix of time series following the source points using MATLAB's column-wise linear index ordering