What is Gwyddion?
"Gwyddion is a modular program for SPM (scanning probe microscopy) data visualization and analysis. Primarily it is intended for analysis of height fields obtained by scanning probe microscopy techniques (AFM, MFM, STM, SNOM/NSOM) " (http://gwyddion.net/)
saveasgsf saves a NxM Matrix in the Gwyddion Simple Field file format (.gsf) (one Channel only)

saveasgwy saves a NxM or NxMxL Matrix in the Gwyddion native file format (.gwy)

Function call:
saveasgsf(filename,data,numstepsx,numstepsy,startx,endx,starty,endy,label,unit,time,varargin)
or
saveasgwy(filename,data,numstepsx,numstepsy,startx,endx,starty,endy,label,unit,time,varargin)

Examples:
saveasgsf('test.gsf',rand(30,200),200,30,1,2,3,4,'Chan1','V',now);
saveasgsf('test.gsf',rand(30,200),200,30;
saveasgwy('test.gwy',rand(30,200,2),200,30,1,2,3,4,{'test1','test2'},{'V','m'},now);

Want to help to improve the code?
=> https://github.com/jensb89/Matlab2Gwyddion