How can I export bathymetry matlab file to shapefile o geotiff format?

Hi everybody, I am new to matlab and I have a bathymetry.mat with several structures: grd = (x,y,dp,dp2 arrays of: [6560x10814 double]),lb =(x,y [52403x1double]), lb1 =(x,y [9x1 double]), lb2 =(x,y [9x1 double]),..... so, I would like to export it to shapefile o geotiff format, but I do not get it yet. I am trying to use shapefilewrite and geotiffwrite but I do not know how I must write the function:My data do not have a geometry field How can I do this?? to Introduce a geometry field in my data and to write the sentence??, because I think I have to use the structure grd. Can anyone please help me how to export it to arcgis?? thanks, Belen