Why is the inv function not working in this code (simple)

m=[cos(-90*pi/180)-cos(30*pi/180) 1;cos(-135*pi/180)-cos(45*pi/180) 1; cos(-180*pi/180)-cos(70*pi/180) 1];

r=[cos(120*pi/180); cos(180*pi/180); cos(250*pi/180)];

k=inv(m)*r;a(1)= 1/k(1); a(3)=1/k(2);

t1=1/k(1)^2;t2=1/k(2)^2;t3=2*k(3)/k(1)*k(2));a(2)=(t1+t2+1-t3)^.5;

thank you!

Answer 1

[James Tursa]

Best to put commas in your matrix difinition so that the parser doesn't inadvertently combine things that you didn't want. E.g., (assuming you wanted a 3x3 instead of a 3x2 matrix result)

>> m=[cos(-90*pi/180)-cos(30*pi/180) 1;cos(-135*pi/180)-cos(45*pi/180) 1; cos(-180*pi/180)-cos(70*pi/180) 1]
m =
   -0.8660    1.0000
   -1.4142    1.0000
   -1.3420    1.0000
>> m=[cos(-90*pi/180),-cos(30*pi/180), 1;cos(-135*pi/180),-cos(45*pi/180), 1; cos(-180*pi/180),-cos(70*pi/180), 1]
m =
    0.0000   -0.8660    1.0000
   -0.7071   -0.7071    1.0000
   -1.0000   -0.3420    1.0000

That being said, this operation with inv( )

>> k=inv(m)*r
k =
    1.3568
    2.8907
    2.0035

is better performed using the backslash operator:

>> k=m\r
k =
    1.3568
    2.8907
    2.0035

You rarely need to use the inv( ) function in MATLAB.

[Delta]

thank you thats great!