function [xOut,yOut,zOut]=gensurf(fis,inputs,output,grids,refInput)
%GENSURF Generate an FIS output surface.
%   Synopsis
%   gensurf(fis)
%   gensurf(fis,inputs,output)
%   gensurf(fis,inputs,output,grids,refinput)
%   
%   Description
%   gensurf(fis) generates a plot of the output surface of a given fuzzy
%   inference system (fis) using the first two inputs and the first output.
%
%   gensurf(fis,inputs,output) generates a plot using the inputs (one or two)
%   and output (only one is allowed) given, respectively, by the vector,
%   inputs, and the scalar, output.
%
%   gensurf(fis,inputs,output,grids) allows you to specify the number of grids
%   in the X (first, horizontal) and Y (second, vertical) directions. If grids
%   is a two element vector, the grids in the X and Y directions can be set
%   independently.
%
%   gensurf(fis,inputs,output,grids,refinput) can be used if there are more 
%   than two outputs. The length of the vector refinput is the same as the 
%   number of inputs. Use NaNs for the entries of refinput corresponding to the 
%   inputs whose surface is being displayed, and real double values to fix the 
%   values of other inputs. 
%
%   [x,y,z]=gensurf(...) returns the variables that define the output surface
%   and suppresses automatic plotting.
% 
%   Examples
%   a = readfis('tipper');
%   gensurf(a)
%
%   See also SURFVIEW, EVALFIS.

%   Ned Gulley, 9-15-94
%   Copyright 1994-2002 The MathWorks, Inc. 
%   $Revision: 1.18 $  $Date: 2002/04/14 22:21:55 $

% Error checking
numInputs=length(fis.input);
numOutputs=length(fis.output);

if numInputs<1, error('System has no inputs.'); end
if numOutputs<1, error('System has no outputs.'); end
if nargin<1, error('No system specified'); end
x=[];
y=[];
z=[];
if nargin<2,
    if numInputs>1,
        inputs=[1 2];
    else
        inputs=1;
    end
end

if nargin<3, output=1; end;
if nargin<4, grids=15; end;

% If no reference input has been provided, let the reference input equal the
% middle of each input variable's range
inRange=getfis(fis,'inRange');
if nargin<5,
    refInput=mean(inRange');
end

if length(inputs)>2,
    error('No more than two input.');
elseif length(inputs)==1,
    xIndex=inputs(1); yIndex=[];
else
    xIndex=inputs(1); yIndex=inputs(2);
end
if length(output)>1,
    error('No more than one output.');
end
zIndex=output;

if length(grids)>2,
    error('No more than two grid values.');
elseif length(grids)==1,
    xGrids=grids(1); yGrids=xGrids;
else
    xGrids=grids(1); yGrids=grids(2);
end

% if yIndex is empty then xzFlag is true
if isempty(yIndex),
    xzFlag=1;
else
    xzFlag=0;
end

% Prepare the input

if xzFlag,
    x=linspace(inRange(xIndex,1),inRange(xIndex,2),xGrids)';
    u=refInput(ones(prod(size(x)),1),:);
    u(:,xIndex)=x(:);
else
    xRange=linspace(inRange(xIndex,1),inRange(xIndex,2),xGrids);
    yRange=linspace(inRange(yIndex,1),inRange(yIndex,2),yGrids);
    [x,y]=meshgrid(xRange,yRange);

    u=refInput(ones(prod(size(x)),1),:);
    u(:,xIndex)=x(:);
    u(:,yIndex)=y(:);
end

% Evaluate the input
v=evalfis(u,fis);

% Prepare the output
v=v(:,zIndex);
z=reshape(v,size(x,1),size(x,2));

% If no output is specified, plot the results
if nargout>1,
    xOut=x; yOut=y; zOut=z;
else
    inLabels=getfis(fis,'inLabels');
    outLabels=getfis(fis,'outLabels');
    if xzFlag,
        plot(x,z);
        xlabel(deblank(inLabels(xIndex,:)));
        ylabel(deblank(outLabels(zIndex,:)));
    else
        surf(x,y,z);
        xlabel(deblank(inLabels(xIndex,:)));
        ylabel(deblank(inLabels(yIndex,:)));
        zlabel(deblank(outLabels(zIndex,:)));
        xMin=min(min(x)); xMax=max(max(x));
        yMin=min(min(y)); yMax=max(max(y));
        zMin=min(min(z)); zMax=max(max(z));
        if zMin==zMax, zMin=-inf; zMax=inf; end;
        axis([xMin xMax yMin yMax zMin zMax])
    end
end