Question

I’m making some matrix computation in matlab. What looks strange (to me) is that I get results like

(8700286382685973*cos(q5)*sin(q4))/9007199254740992 + sin(q5)*((43220913799951902644522757965203*cos(q4))/730750818665451459101842416358141509827966271488 - 291404338770025/1125899906842624)

but matlab does not simplify the result. I already tried to use functions like simplify, simple,fix but none of them gave the desired result.

Any suggestion on what function should I use?

Answer 1

As @Lucas suggested, you can use vpa and digits in matlab, for example if the expression above is A (sym) then:

 vpa(A,3) % digits is set to 3

 ans = 

  0.966*cos(q5)*sin(q4) + sin(q5)*(5.91e-17*cos(q4) - 0.259)

And then you can either see the numbers for themselves and chop them, or use something like:

 function result = significant(x, n)
 % significant(x, n) rounds number x to n number of significant figures

 s = floor(log10(abs(x)));
 shift = 10^(n-1);
 mant = round(x*shift/(10^s)) / shift;
 result = mant * 10^s;