ZF = zeropadf(F) applies zero padding to vector/scalar field(s) F, such 
that ZF is a square field of side given by the largest dimension of F. 
It adds borders of zeros on each sides of the initial rectangle. 
 
This function is useful with spec2f, which requires square fields 
 

truncf, extractf, rotatef, resizef, flipf, shiftf, remapf. 
Published output in the Help browser 
   showdemo zeropadf