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--- gams:difference_between_the_-operator_and_the_power_function [2008/04/02 17:49]
Franz Nelissen
+++ gams:difference_between_the_-operator_and_the_power_function [2008/07/26 05:49] (current)
support
@@ Line 1: / Line 1: @@
 ====== What is the difference between the ** operator and the power function? ======
-The power function ''power(x,y)'' is an integer power and thus the exponent y must be an integer.
+The power function ''power(x,y)'' is an integer power and thus the exponent ''y'' must be an integer.
-This is not required for the %%**%% operator.  %%x**y%% is a real power and gets evaluated as exp(y*log(x)).
+This is not required for the %%**%% operator.  %%x**y%% is a real power and gets evaluated as ''exp(y * log(x))''. The real power is not defined for a negative base (e.g. http://www.cppreference.com/stdmath/pow.html) -  ''x'' must be a positive number (or ''y >= 0'', if  ''x = 0'') to avoid an execution error. So:
-However, with the %%**%% operator x must be a positive number (or y >= 0, if  x = 0) to avoid an execution error. So:
 <code>
 scalar test;
@@ Line 11: / Line 10: @@
 display test;
 </code>
-will give you an error:
+will return an error:
 <code>
 **** Exec Error at line 2: rPower: FUNC DOMAIN: x**y, x < 0

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