CAS ? Home issues?

12142018, 05:33 PM
Post: #1




CAS ? Home issues?
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; 

12142018, 07:37 PM
Post: #2




RE: CAS ? Home issues?
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).


12142018, 11:51 PM
Post: #3




RE: CAS ? Home issues?
(12142018 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? 

12152018, 07:03 AM
Post: #4




RE: CAS ? Home issues?
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. 

12152018, 03:51 PM
Post: #5




RE: CAS ? Home issues?
(12152018 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. 

12152018, 05:46 PM
Post: #6




RE: CAS ? Home issues?
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).


12152018, 08:03 PM
Post: #7




RE: CAS ? Home issues?
(12152018 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. 

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