GSoC 2020 - Week 1

Key highlights of this week’s work are:

• Fixed incorrect limit evaluations caused due to different assumptions of the limit variable

  • In this issue, due to different assumptions of the limit variable, the output was coming out to be different and incorrect for the same limit expression. On digging deep into this issue, we observed that the assumption integer = True was common between all the incorrectly evaluated limit expressions. Thus, we concluded that the Gruntz algorithm is not able to correctly evaluate those expressions where the limit variable possesses integer = True property. So, in order to get all the correct mathematical behaviour from the expression, we decided to define a dummy variable lacking integer = True property. After which, we simply had to substitute the limit variable with this dummy variable for these type of limit expressions to resolve the issue.
    
    

• Fixed incorrect limit evaluations caused due to bug in rewriting

  • At first, this issue seemed tough to resolve because we were unable to find the source of the error. But then, we decided to examine each expression which is generated during evaluation. This helped us to observe that rewriting of the expression was taking place incorrectly and we shifted our focus towards the rewrite() function. Afterwards, it was pretty evident that the xreplace() function utilised for rewriting is not sufficient, as it did not find everything that needs to replaced. Thus, replacing the xreplace() function with the subs() function helped us to resolve this issue.