InterSystems SQL Reference
EXP


A scalar numeric function that returns the exponential (inverse of natural logarithm) of a number.
Synopsis
EXP returns either the NUMERIC or DOUBLE
data type. If
expression is data type DOUBLE,
EXP returns DOUBLE; otherwise, it returns NUMERIC.
EXP is the exponential function
en, where
e is the constant 2.718281828. Therefore, to return the value of
e, you can specify
{fn EXP(1)}.
EXP is the inverse of the natural logarithm function
LOG.
EXP returns a value with a precision of 36 and a scale of 18.
EXP returns NULL if passed a NULL value.
EXP can only be used as an ODBC scalar function (with the curly brace syntax).
The following example returns the constant
e:
SELECT {fn EXP(1)} AS e_constant
The following Embedded SQL example returns the exponential values for the integers 0 through 10:
SET a=0
WHILE a<11 {
&sql(SELECT {fn EXP(:a)} INTO :b)
IF SQLCODE'=0 {
WRITE !,"Error code ",SQLCODE
QUIT }
ELSE {
WRITE !,"Exponential of ",a," = ",b
SET a=a+1 }
}
The following Embedded SQL example demonstrates that
EXP is the inverse of
LOG:
SET x=7
&sql(SELECT {fn EXP(:x)} AS Exp,
{fn LOG(:x)} AS Log,
{fn EXP({fn LOG(:x)})} AS ExpOfLog
INTO :a,:b,:c)
IF SQLCODE'=0 {
WRITE !,"Error code ",SQLCODE
QUIT }
ELSE {
WRITE "Exponential of ",x," = ",a,!
WRITE "Natural log of ",x," = ",b,!
WRITE "Exp of Log of ",x," = ",c
}
Note in the third function call the small discrepancy between the number input and the calculated return value. The next example shows how to handle this computational discrepancy.
The following Embedded SQL example shows the relationship between the
LOG and
EXP functions for the integers 1 through 10:
SET a=1
WHILE a<11 {
&sql(SELECT {fn LOG(:a)} INTO :b)
IF SQLCODE'=0 {
WRITE !,"Error code ",SQLCODE
QUIT }
ELSE {
WRITE !,"Logarithm of ",a," = ",b }
&sql(SELECT ROUND({fn EXP(:b)},12) INTO :c)
IF SQLCODE'=0 {
WRITE !,"Error code ",SQLCODE }
ELSE {
WRITE !,"Exponential of log ",b," = ",c
SET a=a+1 }
}
Note that the
ROUND function is needed here to correct for very small discrepancies caused by system calculation limitations. In the above example,
ROUND is set arbitrarily to 12 decimal digits for this purpose.


ObjectScript function:
$ZEXP