Function File: [ YY,PS] = mapstd (XX,ymean,ystd)

Map values to mean 0 and standard derivation to 1.

          [YY,PS] = mapstd(XX,ymean,ystd)
          
             Apply the conversion and returns YY as (YY-ymean)/ystd.
          
          [YY,PS] = mapstd(XX,FP)
          
             Apply the conversion but using an struct to inform target mean/stddev.
             This is the same of [YY,PS]=mapstd(XX,FP.ymean, FP.ystd).
          
          YY = mapstd('apply',XX,PS)
          
             Reapply the conversion based on a previous operation data.
             PS stores the mean and stddev of the first XX used.
          
          XX = mapstd('reverse',YY,PS)
          
             Reverse a conversion of a previous applied operation.
          
          dx_dy = mapstd('dx',XX,YY,PS)
          
             Returns the derivative of Y with respect to X.
          
          dx_dy = mapstd('dx',XX,[],PS)
          
             Returns the derivative (less efficient).
          
          name = mapstd('name');
          
             Returns the name of this convesion process.
          
          FP = mapstd('pdefaults');
          
             Returns the default process parameters.
          
          names = mapstd('pnames');
          
             Returns the description of the process parameters.
          
          mapstd('pcheck',FP);
          
             Raises an error if FP has some inconsistent.