How good is the trial version

Questions
, ,
1

Hi ! For solving a simple 3 x 3 system of differential equations of second order Mathematica seems to bug. It solves a 2 x 2 , but it fails for larger systems. Should I rely on a trial version ?

2

Calculus in the Trial and Standard versions of Mathematica is the same.

Could you provide the input code? What are the symptoms of failure?
Attaching a notebook file with the inputs and outputs may be the simple way to provide this.

It would help if you include the output of

$Version

evaluated in your Mathematica.

3

Thank you, Bruce.

4

This is a 2 x 2 system that I could solve.

5

However, by using those same commands, solution for this 3 x 3 is not possible, because right after
sol = DSolve[system, {Va, Vb, Vc}, x], the following message appears:

DSolve::deqn: Equation or list of equations expected instead of 230940.11` in the first argument {{(Va^\\),(Vb^\\),(Vc^\\)}=={(-1.1172+0.103897 I) Va-(0.0154234 -0.012988 I) Vb-(0.0136832 -0.0154847 I) Vc,(-0.0170535+0.0107367 I) Va-(1.1124 -0.122354 I) Vb-(0.0170535 -0.0107367 I) Vc,(-0.0136832+0.0154847 I) Va-(0.0154234 -0.012988 I) Vb-(1.1172 -0.103897 I) Vc},230940.,<<4>>,273.001 +65.1873 I}. >>

6

It´s funny to notice that if program 2 x 2 runs for the first tiem, it is perfect. But i I try to run it again it gives de the following message :

DSolve::deqn: Equation or list of equations expected instead of False in the first argument {{(Va^\\),(Vb^\\)}=={(0.8 -3. I) Va-(0.6 -5. I) Vb,(-0.001+4. I) Va-(0.008 -7. I) Vb},False,False,False,False}. >>

Right after the command “sol = DSolve[system, {Va, Vb}, x]” . I judge it may be a bug. And this same bug may be responsible for the fail/error of the 3 x 3 program …

I have Windows 8 and my computer is pretty new .

7

I have no doubt that this is a very simple system and Mathematica should solve it easily. However, I tried to solve it through Laplace Transforms and the problem was similar.

8

By the way, I have the following version : 9.0.1.0 , Platform : Microsoft Windows (64-bit).

9

???

10

Equations need to be specified with Equal (==) and not Set (=), which does assignment. After correcting this, if there has already been an assignment, these variables need to be cleared or the kernel restarted before trying again.

4-29-20149-20-28AM.png
4-29-20149-20-28AM.png645Ă—233 6.58 KB

11

Thank you so much. Ilian ! Now I´m gonna check the coherence of results !

12

Mein Gott ! It fails completely ! Solution cannot present sin and cos terms like . On the other hand, plotted graphics are completely incoherent…

13

By teh way, I tried to solve this same system through Lapalce Transform and result was farther coherent, although not completely…