equivalent assume() in R2011 version

hi,

what is the equivalent of assume() function, to define some condition for resolving a systeme of equation?

Answer 1

[Walter Roberson]

   evalin(symengine, 'assume(TheCondition)')

or

   feval(symengine, 'assume', TheCondition)

[studentU]

thank's for ure repply,

i had try it, but it's doesn't accept symbolic argument!

??? Undefined function or method 'evalin' for input arguments of type 'sym'.

[Walter Roberson]

Try

s = symengine
evalin(s, 'Pi')

and show the result

[studentU]

this is the result:

 s = symengine
 evalin(s, 'Pi')

 s = 

 MuPAD symbolic engine

 ans =

Pi,

so, my problem is to find a and b; / -pi<a<pi and -pi/2<b<pi/2;

i had try :

syms G F X2 X3 el a b

[a,b] = solve('G*cos(y)+F*sin(y)=1',' cos(y)*sin(el)-sin(y)*X2*cos(x)-sin(y)*X3*sin(x)=1','-pi/2<b','b<pi/2','-pi<a','a<pi');

it's generate the error;

and i try to refine the parameter when i evaluate it:

syms G F X2 X3 el a b

[a,b] = solve('G*cos(y)+F*sin(y)=1',' cos(y)*sin(el)-sin(y)*X2*cos(x)-sin(y)*X3*sin(x)=1')

evalin(a,'-pi<a & a<pi');

but isn't the true way! have u a another proposition?

in this case, can i use fminbnd() function, and how can i use it?

[Walter Roberson]

    syms G F X2 X3 el a b x y
    evalin(symengine, 'assume(-PI < a and a < Pi and -PI/2 < b and b < PI/2');
    [a, b] = solve(G*cos(y)+F*sin(y) - 1, cos(y)*sin(el)-sin(y)*X2*cos(x)-sin(y)*X3*sin(x) - 1, a, b);

You should still expect poor results, as you are trying to solve for the value of two variables, a and b, that do not appear in the equations.

If you were to change the x and y to a and b, a solution is possible. However, the solution would be in terms of the F, G, el, X2, X3 variables, and unless you put assumptions on those variables (especially on F and G) it is not possible to figure out where the values would end up.

Supposing that you are trying to solve for x and y instead of a and b, then there are four solutions under the assumptions of real values. The code to generate them is:

t1 = (G ^ 2);
t2 = (F ^ 2);
t5 = sqrt((t1 * (t2 + t1 - 1)));
t6 = F + t5;
t8 = sin(el);
t9 = t8 ^ 2;
t12 = 2 * t9 * t5 * F;
t16 = ((t2 + 1) * t1 + t2 - 1) * t9;
t17 = X2 ^ 2;
t18 = X3 ^ 2;
t19 = (t17 + t18);
t20 = G - 1;
t21 = t20 ^ 2;
t23 = G + 1;
t24 = t23 ^ 2;
t25 = t19 * t21 * t24;
t29 = sqrt(-(-t12 + t16 - t25) * t18 * t1);
t30 = X2 * t6 * t29;
t31 = t18 * t8;
t32 = t20 * t23;
t33 = F * t5;
t34 = t33 - t1;
t36 = t31 * t32 * t34;
t38 = 1 / t19;
t40 = 1 / t6;
t43 = 1 / G;
t46 = 1 / (t1 - 1);
t47 = 1 / X3 * t43 * t46;
t51 = F * t1 * X2 * t8;
t53 = t8 * t5 * X2;
t56 = t43 * t46;
t59 = 1 / (t2 + t1);
t71 = F - t5;
t76 = sqrt(-t18 * (t12 + t16 - t25) * t1);
t77 = X2 * t71 * t76;
t78 = t33 + t1;
t80 = t31 * t32 * t78;
t83 = 1 / t71;

x1 = atan2((-t30 - t36) * t38 * t40 * t47, (-t51 + t53 + t29) * t38 * t56);
x2 = atan2((t30 - t36) * t38 * t40 * t47, (-t51 + t53 - t29) * t38 * t56);
x3 = atan2((-t77 + t80) * t38 * t83 * t47, (-t51 - t53 + t76) * t38 * t56);
x4 = atan2((t77 + t80) * t38 * t83 * t47, (-t51 - t53 - t76) * t38 * t56);
y1 = atan2(t6 * t59, -t34 * t59 * t43);
y2 = y1;
y3 = atan2(t71 * t59, t78 * t59 * t43);
y4 = y3;

Here the solution pairs are [x1,y1], [x2,y2], [x3,y3], [x4,y4]