Need some help using solve

Hello everybody,

I'm facing some troubles trying to use the solve function. I'm getting the wrong value. I did all the calculations on paper and I'm getting a different answer.

So, here is my code:

a1 = 2.3; % cm cubicos
a2 = 2.3; % cm cubicos
a3 = 2.3; % cm cubicos
a4 = 2.3; % cm cubicos
A1 = 730; % cm cubicos
A2 = 730; % cm cubicos
A3 = 730; % cm cubicos
A4 = 730; % cm cubicos
v1 = 0.6; % 60% = 60/100 = 0.6
v2 = 0.6; % 60% = 60/100 = 0.6
k1 = 5.51; % cm cubicos / segundo
k2 = 6.58; % cm cubicos / segundo
g = 981; % cm / segundo ao quadrado
gama1 = 0.333;
gama2 = 0.307;
gama3 = 0.333; % gama3 = 1 - gama4
gama4 = 0.667; % gama4 = 1 - gama1

syms h4;

rh4 = solve((-a4/A4)*(2*g*h4)^(0.5) + ((gama4*k1)/A4)*v1, h4);
disp(h4);

So, if you do the math on paper, you expect to find h4 = 0.000468492

But the matlab is giving me h4 = 17953715759368072310851915890294825625/38322307732477017073753209451412474298368

So, does anyone know what is going on?

Answer 1

[Walter Roberson]

By default, MuPAD converts all numeric values to rationals. You have been given the rational solution to your solve(). IF you want to see the floating point solution, then use double(h4)

Answer 2

[Jacques Vernin]

Is it in MuPad? In MuPad notebook:

a1 := 2.3 ;

a2 := 2.3;

a3 := 2.3;

a4 := 2.3;

A1 := 730;

A2 := 730;

A3 := 730; A4 := 730;

v1 := 0.6;

v2 := 0.6;

k1 := 5.51;

k2 := 6.58;

g := 981;

gama1 := 0.333:

gama2 := 0.307:

gama3 := 0.333;

gama4 := 0.667;

rh4 := solve((-a4/A4)*(2*g*h4)^(0.5) + ((gama4*k1)/A4)*v1, h4): print(rh4):

rh5:= solve(-a4/A4*sqrt(2*g*h)+gama4*k1*v1/A4,h): print(rh5):

rh6:= 1/(2*g)*(gama4*k1*v1/a4)^2: print(rh6)

rh4 is yours, rh5 is the same, simpler, rh6 is the explicit solution. All are 0.000468492