Functions to make combining gradients easier

Is your feature request related to a problem? Please describe. When I am coding oblique gradients, and with multiple types of gradients being played together, there is a need to add gradients together, scale gradients, or change the channels of an already made gradient object.

A typical example is when readout, phase encoding, and slice refocusing gradients overlap. It's straightforward when orthogonal encoding is used - each type would corresponding to one channel (either 'x', 'y', or 'z'). However, when you want general oblique encoding, each type has components in x, y, and z. The add_block function, however, only accepts one gradient per channel (it overwrites the previous one if more than one is used).
Scaling: in radial k-space readouts, for example, you'd want to scale the x and y gradients while maintaining their shape. Right now, existing sequences simply create new gradients each iteration. It would be nice to have functions dedicated to scaling gradients and changing their channels as part of PyPulseq.

Describe the solution you'd like Include these utility functions:

Gradient scaling / channel modification. Returns a changed copy of the input gradient. Detects violations of max gradient or max slew rate and raises corresponding errors.
Combining any number of gradients with arbitrary channels into 3: gx,gy, and gz. Preserve trapezoidal gradients if timings match. Otherwise, return general gradients.
Detect zero gradients during add_block: don't include them to reduce storage waste

Describe alternatives you've considered The alternative is for each user to perform these actions in their custom code, individually. I believe they are generally useful enough to be part of Pypulseq.

imr-framework / pypulseq

Functions to make combining gradients easier #41