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

2018 11 18
2 个回答
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更新时间：2018 11 18
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0 个投票

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;

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madhan ravi
madhan ravi 2018-11-18
InverseRR is a function defined by you? if so upload it
Yi-Le Li
Yi-Le Li 2018-11-18
编辑：madhan ravi 2018-11-18
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
madhan ravi 2018-11-18
you didn't provide the value for ddXa,ddYa
Yi-Le Li
Yi-Le Li 2018-11-18
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
Stephen23 2018-11-18
@Yi-Le Li: please show the complete error message. This means all of the red text.
madhan ravi
madhan ravi 2018-11-18
@Yi no you will still have error see my answer below
Yi-Le Li
Yi-Le Li 2018-11-18
@Stephen Cobeldick
>> Q7
Error: File: Q7.m Line: 12 Column: 2
An array for multiple LHS assignment cannot contain expressions.

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 采纳的回答

Bruno Luong
Bruno Luong 2018-11-18
编辑：Bruno Luong 2018-11-18

0 个投票

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

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Yi-Le Li
Yi-Le Li 2018-11-18
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
Bruno Luong 2018-11-18
it means you get the error! Parenthesis on LHS is not valid syntax so why you ask me the meaning?
Yi-Le Li
Yi-Le Li 2018-11-18
Oh!!Got it !! I'm a new matlab learner.
Thank you so much for helping me solve it !!

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更多回答（1 个）

madhan ravi
madhan ravi 2018-11-18
编辑：madhan ravi 2018-11-18

0 个投票

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

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Stephen23
Stephen23 2018-11-18
"The problem in your code was you put comma ( , ) instead of semicolon ( ; )"
Where? And why is this a problem?

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