{"id":164757,"date":"2023-03-17T08:58:36","date_gmt":"2023-03-17T08:58:36","guid":{"rendered":"\/knowledge\/forums\/topic\/when-trying-to-calculate-the-difference-between-a-variable-at-different-timesteps-i-get-the-error-userd_get_var_value_at_specific-routine-not-implemented-for-this-user-defined-reader\/"},"modified":"2023-07-31T12:26:12","modified_gmt":"2023-07-31T12:26:12","slug":"when-trying-to-calculate-the-difference-between-a-variable-at-different-timesteps-i-get-the-error-userd_get_var_value_at_specific-routine-not-implemented-for-this-user-defined-reader","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/when-trying-to-calculate-the-difference-between-a-variable-at-different-timesteps-i-get-the-error-userd_get_var_value_at_specific-routine-not-implemented-for-this-user-defined-reader\/","title":{"rendered":"When trying to calculate the difference between a variable at different timesteps I get the error: USERD_get_var_value_at_specific routine not implemented for this user defined reader!"},"content":{"rendered":"<p>The error message &#8220;USERD_get_var_value_at_specific routine not implemented for this user defined reader!&#8221; can appear when an user tries to calculate the difference of a variable between two different timesteps in the form:  myDiff = myVar \u00e2\u20ac\u201c myVar{0}  where the current step solution is compared with the first timestep solution.  The error is connected to how EnSight handles the transient data. In order to avoid the issue, one can do instead  myVarT0 = myVar{0}  myDiff = myVar &#8211; myVarT0  In this way the calculation is also more efficient since myVar{0} is stored and EnSight would not have to load the first time-step data for every successive calculation in different instants in time.   Similar considerations apply to the case below  myDiff = myVar{8} &#8211; myVar{2}  that can be replaced as  var1 = myVar{8} var2 = myVar{2} myDiff = var1 &#8211; var2    Keywords: EnSight, Error, USERD_get_var_value_at_specific, Timesteps, Transient, Difference<\/p>\n","protected":false},"template":"","class_list":["post-164757","topic","type-topic","status-publish","hentry","topic-tag-10-2","topic-tag-calculate-variables","topic-tag-ensight","topic-tag-fluid-dynamics","topic-tag-transient"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"The error message &quot;USERD_get_var_value_at_specific routine not implemented for this user defined reader!&quot; can appear when an user tries to calculate the difference of a variable between two different timesteps in the form: myDiff = myVar \u00e2\u20ac\u201c myVar{0} where the current step solution is compared with the first timestep solution. 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