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gams:difference_between_the_-operator_and_the_power_function [2008/04/02 17:55]
Franz Nelissen
gams:difference_between_the_-operator_and_the_power_function [2008/07/26 05:49]
support
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 ====== What is the difference between the ** operator and the power function? ====== ====== 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 in that case x must be a positive number (or y >= 0, if  x = 0) to avoid an execution error. So: +
 <​code>​ <​code>​
 scalar test;  scalar test; 
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 display test;  display test; 
 </​code>​ </​code>​
-will give you an error: ​+will return ​an error: ​
 <​code>​ <​code>​
 **** Exec Error at line 2: rPower: FUNC DOMAIN: x**y, x < 0 **** Exec Error at line 2: rPower: FUNC DOMAIN: x**y, x < 0
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