LOG1PX Function

Returns the log of 1 plus the argument.

Categories:	Mathematical
Categories:	CAS

Table of Contents

Syntax

LOG1PX(x)

specifies a numeric variable, constant, or expression.

The LOG1PX function computes the log of 1 plus the argument. The LOG1PX function is mathematically defined by the following equation, where –1 < x:

When x is close to 0, LOG1PX(x) can be more accurate than LOG(1+x).

The following example computes the log of 1 plus the value 0.5.

data _null_;
   x=log1px(0.5);
   put x=;
run;

data _null_;
   x=log1px(0.5);
   put x=;
run;

SAS writes the following output to the log:

x=0.4054651081

In the following example, the value of X is computed by using the LOG1PX function. The value of Y is computed by using the LOG function.

data _null_;
   x=log1px(1.e-5);
   put x= hex16.;
   y=log(1+1.e-5);
   put y= hex16.;
run;

data _null_;
   x=log1px(1.e-5);
   put x= hex16.;
   y=log(1+1.e-5);
   put y= hex16.;
run;

SAS writes the following output to the log:

x=3EE4F8AEA9AE7317
y=3EE4F8AEA9AF0A25