stepfunc

  STEPFUNC - Evaluate a discrete step function at many times

   [SI,INDS] = STEPFUNC(T, STEPS, TI [,OUTOFBOUNDS])

    Returns the value of a step function that takes values
        STEPS(i) between the times T(i) and T(i+1).
        (STEPS(end) is assumed to be true between
          T(end) and T(end)+mean(diff(T)) )

    If OUTOFBOUNDS is provided, one can specify the value of
    SI when ti is out of bounds.  Default is NaN; example
    choices might be NaN or 0.

    INDS are the index values such that
    SI = STEPS(INDS); INDS that are out of bounds are 
      NaN.

    STEPS can have many rows; each row will be one step
    function, and the answer will have the same number of
    rows as STEPS; the columns of SI will be the same number as ti.

    Example 1:  Evaluate a step function at a high sampling rate
       S = [ 0 1 2 3 4 5 6 7 8 9 10]; % steps
       t = [ 0:0.1:1 ] ; % steps each 0.1 seconds
       ti = [ 0:0.001:1 ];
       Si = stepfunc(t,S,ti); 
       figure;
       plot(ti,Si);  % plots at high temporal resolution
       xlabel('X-axis');
       ylabel('Value');

    Example 2: Evaluate a step function at a few locations:
       S = [ 0 1 2 3 4 5 6 7 8 9 10]; % steps
       t = [ 0:0.1:1 ] ; % steps each 0.1 seconds
       ti= [ 0 0.05 0.9 1.1];
       [Si,inds] = stepfunc(t,S,ti)

        gives 

            Si   : [0 0 9 NaN]
            inds : [1 1 10 NaN]