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CAS ? Home issues? - toshk - 12-14-2018 05:33 PM
inverse matrix; in CAS; [undef] Home; correct ans; [[(1/2585000000000)*((e^(1/517))^15034+(e^(1/517))^1551),(-1/2585000000000)*e^3,0,(-1/2585000000000)*e^(15034/517),1],[(-1/2585000000000)*e^3,(1/2585000000000)*(e^3+1292500000),-1/2000,0,0],[0,-1/2000,3/2000,-1/2000,0],[(-1/2585000000000)*e^(15034/517),0,-1/2000,(1/2585000000000)*(e^(15034/517)+1292500000),0],[1,0,0,0,0]]^(-1) also seen issues with LSQ function as well in CAS; RE: CAS ? Home issues? - parisse - 12-14-2018 07:37 PM
There is an exponent overflow trying to do exact computation (because of the exp()^...). Add a point to any integer and you'll get an answer in CAS. The answer in CAS is a little bit more precise (try to multiply by the original matrix). RE: CAS ? Home issues? - toshk - 12-14-2018 11:51 PM
(12-14-2018 07:37 PM)parisse Wrote: There is an exponent overflow trying to do exact computation (because of the exp()^...). Add a point to any integer and you'll get an answer in CAS. The answer in CAS is a little bit more precise (try to multiply by the original matrix).Thanks, exp()^......is of order(Is*exp(V/Vth)-1), chosen for the exact numerical computation in CAS. And CAS want approx representation now? The matrix represent here is computation in application and i do not the luxury to add a point. how do i add a point without approx in application? RE: CAS ? Home issues? - parisse - 12-15-2018 07:03 AM
Run inv(evalf(...)) Or use only rationals. If you are using exp(), computations are done with exp replaced by a formal parameter, computing with polynomials. The degree of polynomial can not be too large otherwise computations would last too long and take too much memory. RE: CAS ? Home issues? - CyberAngel - 12-15-2018 03:51 PM
(12-15-2018 07:03 AM)parisse Wrote: Run inv(evalf(...))Hiw much RAM would be sufficient? 2GB? Unknown, depending on the polynomial. The needed RAM could be calculated, but it's not feasible to do. RE: CAS ? Home issues? - parisse - 12-15-2018 05:46 PM
It's not just a question of RAM, I have set an upper bound for degrees in multivariate polynomials (and it must fit in a short signed int anyway). RE: CAS ? Home issues? - CyberAngel - 12-15-2018 08:03 PM
(12-15-2018 05:46 PM)parisse Wrote: It's not just a question of RAM, I have set an upper bound for degrees in multivariate polynomials (and it must fit in a short signed int anyway). I guess that in all algorithms concerning matrices they are typically uncompressed, meaning: all the individual elements or cells occupy memory. It uses more RAM, but saves CPU and uncomplicates the algorithms. |