error:An array for multiple LHS assignment cannot contain expressions.

Error: File: Q7.m Line: 12 Column: 2

What does the error mean?

I'm using Matlab to solve Mechanism problems,and here is my code.

I'm pretty sure that it's not InverseRR's problem.I have used that function in other problems ,and it worked.

Hope that somebody who good at it could help me,please><

clc
clear

a1 = 15 ; a2 = 30 ; a3 = 20 ; a4 = 30 ; alpha = 30;
Xq = 50 ; Yq = 8 ; Xr = 70 ; Yr = 8;
dXa = 10 ; dYa = 0;
Xa = 20 ;Ya = a1 ;
I = 1;
BC = sqrt(a3^2 + a4^2 - 2 * a3 * a4 * cos(alpha)) ;

[(theta04),(theta02),dtheta4,dtheta2,ddtheta4,ddtheta2] = InverseRR(Xq,Yq,a3,a2,Xa,Ya,dXa,dYa,ddXa,ddYa,I);
theta2 = theta02 - 180;
theta4 = theta04 - alpha;

[madhan ravi]

InverseRR is a function defined by you? if so upload it

[Yi-Le Li]

Yes :(

function[PHI,PSI,dPHI,dPSI,ddPHI,ddPSI] = InverseRR(Xq,Yq,c,b,Xa,Ya,dXa,dYa,ddXa,ddYa,I)

X = Xa - Xq;
Y = Ya - Yq;

A = 2 * c* Y;
B = 2 * c * X;
C = X^2 + Y^2 + c^2 - b^2;

t1 = (A + sqrt(A^2+B^2-C^2))/(C+B);
t2 = (A - sqrt(A^2+B^2-C^2))/(C+B);

if (I == 1)
    t = t1;
else
    t = t2;
end

PHI = 2*atan(t);

U = (X- c*cos(PHI))/b;
V = (Y- c*sin(PHI))/b;

PSI = atan2(V,U);

Xb = c*cos(PHI);
Yb = c*sin(PHI);

%%% Inverse Velocity%%%
dX = dXa;
dY = dYa;

D = [ -c * sin(PHI)  -b * sin(PSI), c * cos(PHI)   b * cos(PSI)  ];
   
E = [ dX,
      dY  ];
  
F = D \ E ;
dPHI = F(1,1);
dPSI = F(2,1);

%%% Inverse Acceleration %%%
ddX = ddXa;
ddY = ddYa;

G = [ -c * sin(PHI)  -b * sin(PSI),
       c * cos(PHI)   b * cos(PSI)  ];
   
H = [ ddX + c * cos(PHI) * dPHI ^2 - b * cos(PSI) * dPSI ^2  ,
      ddY + c * cos(PHI) * dPHI ^2 - b * sin(PSI) * dPSI ^2  ] ;
  
I = G \ H;

ddPHI = I(1,1);
ddPSI = I(2,1);

PHI = PHI / pi * 180;
PSI = PSI / pi * 180;
end

[madhan ravi]

you didn't provide the value for ddXa,ddYa

[Yi-Le Li]

Oh!I think we solved the problem xD

I provided ddXa,ddYa to the code,but it still can't work,and then I delete the Parentheses of theta02 and theta04 , and the error was gone !

Thanks for helping me!!!!

[Stephen23]

@Yi-Le Li: please show the complete error message. This means all of the red text.

[madhan ravi]

@Yi no you will still have error see my answer below

[Yi-Le Li]

@Stephen Cobeldick

>> Q7

Error: File: Q7.m Line: 12 Column: 2

An array for multiple LHS assignment cannot contain expressions.

Answer 1

[Bruno Luong]

Remove the parenthesis

[theta04,theta02,dtheta4,dtheta2,ddtheta4,ddtheta2]  = InverseRR...

[Yi-Le Li]

I tried it ,and it works!!

Thank you :D

But I'm still a little confused about it.Can you tell me what the parentheses here mean?

[Bruno Luong]

it means you get the error! Parenthesis on LHS is not valid syntax so why you ask me the meaning?

[Yi-Le Li]

Oh!!Got it !! I'm a new matlab learner.

Thank you so much for helping me solve it !!

Answer 2

[madhan ravi]

The problem in your code was you put comma ( , ) instead of semicolon ( ; )

Reason see mldivide

a1 = 15 ; a2 = 30 ; a3 = 20 ; a4 = 30 ; alpha = 30;
Xq = 50 ; Yq = 8 ; Xr = 70 ; Yr = 8;
dXa = 10 ; dYa = 0;
Xa = 20 ;Ya = a1 ;
I = 1;
ddXa=3; %fake data change it to your value
ddYa=5; %fake data change it to your value
BC = sqrt(a3^2 + a4^2 - 2 * a3 * a4 * cos(alpha)) ;
%|------||------|----error was here
[theta04,theta02,dtheta4,dtheta2,ddtheta4,ddtheta2] = InverseRR(Xq,Yq,a3,a2,Xa,Ya,dXa,dYa,ddXa,ddYa,I);

theta2 = theta02 - 180;
theta4 = theta04 - alpha;
 
function[PHI,PSI,dPHI,dPSI,ddPHI,ddPSI] = InverseRR(Xq,Yq,c,b,Xa,Ya,dXa,dYa,ddXa,ddYa,I)
X = Xa - Xq;
Y = Ya - Yq;
A = 2 * c* Y;
B = 2 * c * X;
C = X^2 + Y^2 + c^2 - b^2;
t1 = (A + sqrt(A^2+B^2-C^2))/(C+B);
t2 = (A - sqrt(A^2+B^2-C^2))/(C+B);
if (I == 1)
    t = t1;
else
    t = t2;
end
PHI = 2*atan(t);
U = (X- c*cos(PHI))/b;
V = (Y- c*sin(PHI))/b;
PSI = atan2(V,U);
Xb = c*cos(PHI);
Yb = c*sin(PHI);
%%% Inverse Velocity%%%
dX = dXa;
dY = dYa;
D = [ -c * sin(PHI)  -b * sin(PSI); c * cos(PHI)   b * cos(PSI)  ];
                               %  ^--------- error was here
E = [ dX;
      dY  ];
  
F = D \ E ;
dPHI = F(1,1);
dPSI = F(2,1);
%%% Inverse Acceleration %%%
ddX = ddXa;
ddY = ddYa;
G = [ -c * sin(PHI)  -b * sin(PSI); %error was here
       c * cos(PHI)   b * cos(PSI)  ];
   
H = [ ddX + c * cos(PHI) * dPHI ^2 - b * cos(PSI) * dPSI ^2  ; %error was here
      ddY + c * cos(PHI) * dPHI ^2 - b * sin(PSI) * dPSI ^2  ] ;
  
I = G \ H;
ddPHI = I(1,1);
ddPSI = I(2,1);
PHI = PHI / pi * 180;
PSI = PSI / pi * 180;
end

[Stephen23]

"The problem in your code was you put comma ( , ) instead of semicolon ( ; )"

Where? And why is this a problem?