uquiver(varargin)

 function hh = uquiver(varargin)
% Modified version of Quiverc to plots UNIFORM or UNSCALLED velocity vectors 
% as arrows of same length, with components (u,v) at the points (x,y) using 
% the current colormap. 

%   UQUIVER Quiver color plot.
%   UQUIVER(X,Y,U,V) plots velocity vectors as arrows with components (u,v)
%   at the points (x,y).  The matrices X,Y,U,V must all be the same size
%   and contain corresponding position and velocity components (X and Y
%   can also be vectors to specify a uniform grid).  
%
%   UQUIVER(U,V) plots velocity vectors at equally spaced points in
%   the x-y plane.
%
%   UQUIVER(U,V,S) or UQUIVER(X,Y,U,V,S) automatically scales the 
%   arrows to fit within the grid and then stretches them by S.  Use
%   S=0 to plot the arrows without the automatic scaling.
%
%   UQUIVER(...,LINESPEC) uses the plot linestyle specified for
%   the velocity vectors.  Any marker in LINESPEC is drawn at the base
%   instead of an arrow on the tip.  Use a marker of '.' to specify
%   no marker at all.  See PLOT for other possibilities.
%
%   UQUIVER(...,'filled') fills any markers specified.
%
%   H = QUIVERC(...) DOES NOT return the vector of line handles due to 
%   color indexing information.
%
%   Example:
%   load wind
%   x=x(1,:,1); y=y(:,1,1)';
%   [X,Y]=meshgrid(x,y);
%   u=u(:,:,6)*10; v=v(:,:,6)*10;
%   Vmag=sqrt(u.^2+v.^2);
%   uquiver(X,Y,u,v,50)
%   axis image
%   cbar(Vmag,'m/s')
%
%   See also FEATHER, QUIVER3, PLOT. 
%   Clay M. Thompson 3-3-94
%   Bertrand Dano 0
%   Copyright 1984-2009 The MathWorks, Inc. 
%-------------------------------------------------------------

% Arrow head parameters
alpha = 0.33; % Size of arrow head relative to the length of the vector
beta = 0.23;  % Width of the base of the arrow head relative to the length
autoscale = 1; % Autoscale if ~= 0 then scale by this.
plotarrows = 1; % Plot arrows
sym = '';

filled = 0;
ls = '-';
ms = '';
col = '';
lw=1;

nin = nargin;
% Parse the string inputs
while isstr(varargin{nin}),
  vv = varargin{nin};
  if ~isempty(vv) & strcmp(lower(vv(1)),'f')
    filled = 1;
    nin = nin-1;
  else
    [l,c,m,msg] = colstyle(vv);
    if ~isempty(msg), 
      error(sprintf('Unknown option "%s".',vv));
    end
    if ~isempty(l), ls = l; end
    if ~isempty(c), col = c; end
    if ~isempty(m), ms = m; plotarrows = 0; end
    if isequal(m,'.'), ms = ''; end % Don't plot '.'
    nin = nin-1;
  end
end


error(nargchk(2,5,nin));

% Check numeric input arguments
if nin<4, % quiver(u,v) or quiver(u,v,s)
  [msg,x,y,u,v] = xyzchk(varargin{1:2});
else
  [msg,x,y,u,v] = xyzchk(varargin{1:4});
end
if ~isempty(msg), error(msg); end

if nin==3 | nin==5, % quiver(u,v,s) or quiver(x,y,u,v,s)
  autoscale = varargin{nin};
end

% Scalar expand u,v
if prod(size(u))==1, u = u(ones(size(x))); end
if prod(size(v))==1, v = v(ones(size(u))); end

if autoscale,
  % Base autoscale value on average spacing in the x and y
  % directions.  Estimate number of points in each direction as
  % either the size of the input arrays or the effective square
  % spacing if x and y are vectors.
  if min(size(x))==1, n=sqrt(prod(size(x))); m=n; else [m,n]=size(x); end
  delx = diff([min(x(:)) max(x(:))])/n;
  dely = diff([min(y(:)) max(y(:))])/m;
  len = sqrt((u.^2 + v.^2)/(delx.^2 + dely.^2));
  autoscale = autoscale*0.9 / max(len(:));
  u = u*autoscale; v = v*autoscale;
end

%----------------------------------------------
% Define colormap 
vr=sqrt(u.^2+v.^2);

vrn=round(vr/max(vr(:))*64);
CC=colormap;
ax = newplot;
next = lower(get(ax,'NextPlot'));
hold_state = ishold;

%----------------------------------------------
% Make velocity vectors and plot them

x = x(:).';y = y(:).';
u = u(:).';v = v(:).';
vrn=vrn(:).';
u=u./vrn; v=v./vrn;
uu = [x;x+u;repmat(NaN,size(u))];
vv = [y;y+v;repmat(NaN,size(u))];
vrn1= [vrn;repmat(NaN,size(u));repmat(NaN,size(u))];

uui=uu(:);  vvi=vv(:);  vrn1=vrn1(:); imax=size(uui);
hold on

 for i=  1:3:imax-1
    ii=int8(round(vrn1(i)));
    if ii==0; ii=1; end        
    c1= CC(ii,1);    c2= CC(ii,2);    c3= CC(ii,3);
    plot(uui(i:i+1),vvi(i:i+1),'linewidth',lw,'color',[c1 c2 c3]);
end

%----------------------------------------------
% Make arrow heads and plot them

if plotarrows,
 
  hu = [x+u-alpha*(u+beta*(v+eps));x+u; ...
        x+u-alpha*(u-beta*(v+eps));repmat(NaN,size(u))];
  hv = [y+v-alpha*(v-beta*(u+eps));y+v; ...
        y+v-alpha*(v+beta*(u+eps));repmat(NaN,size(v))];
  vrn2= [vrn;vrn;vrn;vrn];

 uui=hu(:);  vvi=hv(:);  vrn2=vrn2(:); imax=size(uui);

 for i=  1:imax-1
    ii=int8(round(vrn2(i)));
    if ii==0; ii=1; end   
    c1= CC(ii,1);    c2= CC(ii,2);    c3= CC(ii,3);
    plot(uui(i:i+1),vvi(i:i+1),'linewidth',lw,'color',[c1 c2 c3]);
 end

else
  h2 = [];
end
%----------------------------------------------

if ~isempty(ms), % Plot marker on base
  hu = x; hv = y;
  hold on
  h3 = plot(hu(:),hv(:),[col ms]);
  if filled, set(h3,'markerfacecolor',get(h1,'color')); end
else
  h3 = [];
end

if ~hold_state, hold off, view(2); set(ax,'NextPlot',next); end

if nargout>0, hh = [h1;h2;h3]; end
set(gca,'Clim',[0 max(vr(:))]);
set(gca, 'color', [0 0 0], 'tickdir','out')
%set(gca, 'color', [0 0 0],'Xcolor','w','Ycolor','w');
%set(gcf, 'color', [0 0 0]);
%set(gcf, 'InvertHardCopy', 'off');