# backtr

## PURPOSE

## SYNOPSIS

function z=backtr(y,fit)

## DESCRIPTION

     Inverse-link transformation of y.

## CROSS-REFERENCE INFORMATION

This function calls:

This function is called by:

- fitted Fitted values from a locfit object.

## SOURCE CODE

    0001 function z=backtr(y,fit)
    0002 %
    0003 % Inverse-link transformation of y.
    0004
    0005 fali = fit.fit_points.family_link;
    0006 link = fali(2);
    0007 switch link
    0008   case 3
    0009     z=y;
    0010   case 4
    0011     z=exp(y);
    0012   case 5
    0013     z = y;
    0014     i = find(y<=0);
    0015     if (length(i)>0)
    0016       z(i) = exp(y(i))./(1+exp(y(i)));
    0017     end;
    0018     i = find(y>0);
    0019     if (length(i)>0)
    0020       z(i) = 1./(1+exp(-y(i)));
    0021     end;
    0022   case 6
    0023     z=1./y;
    0024   case 7
    0025     z=y.*abs(y);
    0026   case 8
    0027     z=sin(y).^2;
    0028   otherwise
    0029      disp('Backtr: invalid link');
    0030      z=y;
    0031 end;
    0032
    0033 return;