Re: Speeding up a plotting function

[Francesco Potortì]

>I have written a simple plotting function, code below, but unfortunately it
>takes some time to plot. Is there any way in which I could speed this up?
>
>function hilo_conditional_plot( high , low , condition )
>%HILO_CONDITIONAL_PLOT
>%   Takes high, low and condition input vectors and plots a line chart of 
>highs 
>%   and lows coloured according to the condtion. For this basic version there
>%   are only 3 conditons; 1 for long, -1 for short and 0 for neutral; with the
>%   respective plot colours being blue, red and green.
>
>date = ( 1 : length(high) )' ;
>hold on ;
>for ii = 1 : length( high )
>   if condition(ii) == 1
>   line( [ date(ii) date(ii) ] , [ low(ii) high(ii) ] , 'Color' , 'b' 
> ,'linewidth' , 2 ) ;
>   elseif condition(ii) == -1
>   line( [ date(ii) date(ii) ] , [ low(ii) high(ii) ] , 'Color' , 'r' 
> ,'linewidth' , 2 ) ;
>   elseif condition == 0
>   line( [ date(ii) date(ii) ] , [ low(ii) high(ii) ] , 'Color' , 'g' 
> ,'linewidth' , 2 ) ;
>   else
>   printf( 'Error in condition vector - a value != 1,-1 or 0' ) ;
>   end
>end
>grid minor on ;
>hold off ;

Dear babelproofreader,

as already suggested, the likely problem is that you call the line()
function a lot of times, which slows things down.  I suggest you do just
three calls to plot(), which should be much faster.  With plot, you can
draw a discontinuous line by including NaN values.

Assuming that low and high are column vectors, it would be something
like that (untried, may contain bugs):

hole = nan(size(date));
xall = [date date hole];
yall = [low high hole];
hold on
for c = [-1 0 1]
    filt = (condition == c);
    x = xall(filt, :)';
    y = yall(filt, :)';
    color = "brg"(c+2);
    plot(x(:), y(:), 'color", color, 'linewidth", 2);
endfor
hold off

condition values not in [-1 0 1] are ignored.

-- 
Francesco Potortì (ricercatore)        Voice:  +39.050.621.3058
ISTI - Area della ricerca CNR          Mobile: +39.348.8283.107
via G. Moruzzi 1, I-56124 Pisa         Skype:  wnlabisti
(entrance 20, 1st floor, room C71)     Web:    http://fly.isti.cnr.it