Too Many Output Arguments

I'm using Matlab to solve for the constrained optimization of f(x,y,z) = 6x+6y+5z with a constraint of 3x^2+3y^2+5z^2 = 29.

My code looks like this:

clc
syms x y z t l
f = 6*x + 6*y +5*z
c = 3*x^2+3*y^2+5*z^2
c1 = 29
gFunc = gradient(f)
gConst = gradient(c)
eqn1 = gFunc(1,1) == l * gConst(1,1)
eqn2 = gFunc(2,1) == l * gConst(2,1)
eqn3 = gFunc(3,1) == l * gConst(3,1)
eqn4 = c == c1
[xsoln,ysoln,zsoln,lsoln] = solve([eqn1,eqn2,eqn3,eqn4],[x,y,z,l])

When I run the code, I get an error in saying that [xsoln,ysoln,zsoln,lsoln] = ... has too many output arguments, but I am solving 4 equations for 4 variables, and want 4 outputs, so I don't see how I am getting this error.

Any tips? Thanks!

Answer 1

[Walter Roberson]

clc
syms x y z t l
f = 6*x + 6*y +5*z

f = 

6 x+6 y+5 z

c = 3*x^2+3*y^2+5*z^2

c = 

3 x2+3 y2+5 z2

c1 = 29

c1 = 29

gFunc = gradient(f)

gFunc = 

665

gConst = gradient(c)

gConst = 

6 x6 y10 z

eqn1 = gFunc(1,1) == l * gConst(1,1)

eqn1 = 

6=6 l x

eqn2 = gFunc(2,1) == l * gConst(2,1)

eqn2 = 

6=6 l y

eqn3 = gFunc(3,1) == l * gConst(3,1)

eqn3 = 

5=10 l z

eqn4 = c == c1

eqn4 = 

3 x2+3 y2+5 z2=29

[xsoln,ysoln,zsoln,lsoln] = solve([eqn1,eqn2,eqn3,eqn4],[x,y,z,l])

xsoln = 

(−22)

ysoln = 

(−22)

zsoln = 

(−11)

lsoln = 

−1212

Works for me in R2020a and R2020b . Which release are you using?

[Walter Roberson]

Sorry about the output format. That last bit really looks like the following:

[Tyler Reohr]

R2020a

I had it working for problems with only [x,y,l] but as soon as I added in z it gave me that error.

It works up to the line that is supposed to give me potential points where it could be a max or min:

[xsoln,ysoln,zsoln,lsoln] = solve([eqn1,eqn2,eqn3,eqn4], [x,y,z,l])

For the results from before that I get:

 
f =
 
6*x + 6*y + 5*z
 
 
c =
 
3*x^2 + 3*y^2 + 5*z^2
 

c1 =

    29

 
gFunc =
 
 6
 6
 5
 
 
gConst =
 
  6*x
  6*y
 10*z
 
 
eqn1 =
 
6 == 6*l*x
 
 
eqn2 =
 
6 == 6*l*y
 
 
eqn3 =
 
5 == 10*l*z
 
 
eqn4 =
 
3*x^2 + 3*y^2 + 5*z^2 == 29

[Tyler Reohr]

Is it possible that it's something with the naming convention I used? I've read that it's possible for Matlab to think you're calling a function within the vector with certain names, but xsoln, ysoln, zsoln, and lsoln aren't any commands I could find.

[Walter Roberson]

What shows up for

which -all solve

[Tyler Reohr]

>> which -all solve
solve is a variable.
C:\Program Files\MATLAB\R2020a\toolbox\symbolic\symbolic\@sym\solve.m  % Shadowed sym method

[Tyler Reohr]

I couldn't get it to work so I reinstalled it to clear the cache or any settings I might have arbitrarily changed on accident. It worked after that so I don't believe it was a problem with the code. Don't know exactly what went wrong, but it's working now. Thanks!

[Walter Roberson]

You had accidentally assigned a value to a variable named solve