Spline Toolbox™

Positive part

Syntax

• xp = subplus(x)
  

Description

xp = subplus(x) returns , i.e., the positive part of x, which is x if x is nonnegative and 0 if x is negative. In other words, xp equals max(x,0). If x is an array, this operation is applied entry by entry.

Examples

Example 1. Here is a plot of the essential part of the subplus function, as generated by

• x = -2:2; plot(x,subplus(x),'linew',4), axis([-2,2,-.5,2.5])
  
  
  

Example 2. The following anonymous function describes the so-called hat function:

• hat = @(x) subplus(x) - 2*subplus(x-1) + subplus(x-2);
  

i.e., the spline also given by spmak(0:2,1), as the following plot shows.

• x = -.5:.5:2.5; plot(x,hat(x),'linew',4), set(gca,'Fontsize',16)
  
  
  

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