Error: The expression to the left of the equals sign is not a valid target for an assignment.

Ycomfort=str2func(strcat('@(x,T_set_r,T_room_m,T_room_mm,DT_m,DT_L,DT_U,T_room,Gt,dc,Q_HVAC,N_slot,T_set_w,dT_L,dT_U,Tw_m,Tw_mm,f_t,G,Bt,Rt,dT_m,T_w,T_env,T_n,Q_CHPU)',Fcomfort));

Error: The expression to the left of the equals sign is not a valid target for an assignment.

[Rik]

Is Ycomfort used prior to this line of code as a variable? Is it used as a function name in that same file? Is it the name of a class on your search path?

[PUPPALA RAJENDHAR 17PHD0038]

befor the line it was not used.no function was used in the same file with name Ycomfort.

After this line it was used in

[x,fval,exitflag] = ga(@(x)MultiObj(x,alpha, daprce, revenue,degcost,NG,nu_e,P_CHPU,T_set_r,T_room_m,T_room_mm,DT_m,DT_L,DT_U,T_room,Gt,dc,Q_HVAC,N_slot,T_set_w,dT_L,dT_U,Tw_m,Tw_mm,f_t,G,Bt,Rt,dT_m,T_w,Q_CHPU,T_env,T_n, Ycost, Ycomfort),ngen,A,b,[],[],lb,ub,[],Binvar(timesteps,[3 4 5 6 7]),optionsGA);

fcomfort = 1/5*(Ycomfort(x,T_set_r,T_room_m,T_room_mm,DT_m,DT_L,DT_U,T_room,Gt,dc,Q_HVAC,N_slot,T_set_w,dT_L,dT_U,Tw_m,Tw_mm,f_t,G,Bt,Rt,dT_m,T_water,T_env,T_n,Q_CHPU)- YnonInt(x) + YnonInt([0 0 0 0 N_start_WM N_start_DW N_start_CD, zeros(1,ngen-7)])) %Total comfort cost

[Rik]

I don't see any direct reasons for your error. Try to make a MWE so we can run your code without any other dependencies and can reproduce your issue.

[PUPPALA RAJENDHAR 17PHD0038]

Thank you sir for your valuable suggestion. i will try to make a MWE

[Walter Roberson]

The most common cause for this problem is that you are in the middle of a [ or { matrix definition, that you forgot a ] or } or accidentally commented it out

Answer 1

[Stephen23]

As Walter Roberson already wrote, the problem is most likely caused by unmatched curly braces or square brackets earlier in the code. This error is easy to demonstrate, e.g. in a script which mimics your code flow:

baz = @(a,b)a+b;
str = 'baz(a,b);';
vec = {1,2,; % !!! unmatched curly brace !!!
foo = str2func(strcat('@(a,b)',str));
foo(2,3)

which when run throws exactly the error that you are getting:

>> temp5
Error: File: temp5.m Line: 6 Column: 5
The expression to the left of the equals sign is not a valid target for an assignment.

Here is a much simpler demonstration of this error, showing that the error is unrelated to str2func or strcat or functions in particular:

vec = {1,2,; % !!! unmatched curly brace !!!
foo = 23

giving:

>> temp5
Error: File: temp5.m Line: 5 Column: 5
The expression to the left of the equals sign is not a valid target for an assignment. 

Solution: check your brackets/braces !

Answer 2

[Mahesh Taparia]

Hi,

You can use the below command:

Ycomfort=str2func('@(x,T_set_r,T_room_m,T_room_mm,DT_m,DT_L,DT_U,T_room,Gt,dc,Q_HVAC,N_slot,T_set_w,dT_L,dT_U,Tw_m,Tw_mm,f_t,G,Bt,Rt,dT_m,T_w,T_env,T_n,Q_CHPU)Fcomfort(varargin)'); 

Where Fcomfort is the function of the mentioned variables.

You can refer the below link for more help for str2func:

https://www.mathworks.com/help/matlab/ref/str2func.html

[Rik]

That doesn't make sense to me. That would be equivalent of the example below.

fun=str2func('@(a,b)plot');
fun(1:10,rand(10,1)) %returns an error

Unless the inner function retrieves the variables from the caller with evalin, I don't see how this would work. Could you further explain your reasoning?

[Mahesh Taparia]

As per my answer, Fcomfort should be a function of the variables which is mentioned in the '@()' , for example:

F=str2func('@(x)x+9')

Your command will work if you try the given below statement:

fun=str2func('@(a,b)plot(a,b)');
 fun(1:10,rand(10,1))

[Stephen23]

"As per my answer, Fcomfort should be a function of the variables which is mentioned in the '@()' ..."

Here is str2func exactly as you used it in your answer:

str2func('@(x,T_set_r,T_room_m,T_room_mm,DT_m,DT_L,DT_U,T_room,Gt,dc,Q_HVAC,N_slot,T_set_w,dT_L,dT_U,Tw_m,Tw_mm,f_t,G,Bt,Rt,dT_m,T_w,T_env,T_n,Q_CHPU)Fcomfort');

and now abbreviated for clarity, showing that you did not call Fcomfort with any input arguments:

str2func('@(x,T_set_r,...,T_n,Q_CHPU)Fcomfort');
%                                    ^^^^^^^^^ Fcomfort does not use any of the variables

"Where Fcomfort is the function of the mentioned variables."

Can you show an example of this working? When I try your advice it fails:

>> F = str2func('@(a,b)baz');
>> F(1,3)
Error using baz (line 2)
Not enough input arguments.
Error in @(a,b)baz

Where baz is "a function of the variables which is mentioned in the '@()'" exactly as you specified:

function z = baz(a,b)
z = a+b;
end

Or even simply:

>> baz = @(a,b)a+b;
>> F = str2func('@(a,b)baz');
>> F(0,1)
Undefined function or variable 'baz'.
Error in @(a,b)baz

"Your command format is incorrect"

Why? It works perfectly when I tried it:

>> baz = @(a,b)a+b;
>> fun = 'baz(a,b)';
>> foo = str2func(strcat('@(a,b)',fun));
>> foo(2,3)
ans =
     5

[Walter Roberson]

This is incorrect information. The original question uses strcat to put together a header and the content of a variable, which is perfectly valid. The suggested form puts the header and the variable name, but executing the variable would just return the content of the character vector, rather than using the character vector as indicating which expression to execute.

[madhan ravi]

This given information is rather confusing, how can it be called without specifying the number of input arguments?

[Stephen23]

@Mahesh Taparia: I am astonished at your lastest edit:

str2func('@(x,T_set_r,T_room_m,T_room_mm,DT_m,DT_L,DT_U,T_room,Gt,dc,Q_HVAC,N_slot,T_set_w,dT_L,dT_U,Tw_m,Tw_mm,f_t,G,Bt,Rt,dT_m,T_w,T_env,T_n,Q_CHPU)Fcomfort(varargin)');

Again, abbreviated for clarity:

tr2func('@(x,T_set_r,...,T_n,Q_CHPU)Fcomfort(varargin)');
%                                            ^^^^^^^^ where is this defined?

Where is varargin defined? When I try your answer, it throws an error:

>> baz = @(a,b)a+b;
>> foo = str2func('@(a,b)baz(varargin)'); % your proposal
>> foo(2,3)
Attempt to execute SCRIPT varargin as a function:
C:\MATLAB\R2012b\toolbox\matlab\lang\varargin.m
Error in @(a,b)baz(varargin)

Even if varargin was correctly specified as an input argument, it seems strange to pass the cell array as one single argument to the called function. Did you forget to use a comma-separated list?

I did not have any problems when I defined varargin properly and used a comma-separated list:

>> foo = str2func('@(varargin)baz(varargin{:})');
>> foo(2,3)
ans =
     5

[Walter Roberson]

Remember that fcomfort is a character vector containing an expression to be executed. Imagine for example a uicontrol edit field that the user was permitted to enter the text of an expression into.

When you include fcomfort literally in the function with (varargin) or (varargin{:}) or listing out the arguments, then the effect would be to try to index the character vector.

The original strcat of the user was correct. The error is from other causes, especially having failed to close a ] on a previous line.

[Mahesh Taparia]

Hi Stephen,

I wrote varargin just to show we need to pass the input arguments of Fcomfort which was not mentioned in the question.

[Rik]

@Mahesh can you try to make an example with your syntax that can actually run without errors? Whenever I get questioning comments from other users, I always make sure that the code I'm suggesting runs at least on my system.

[Walter Roberson]

You can code

Ycomfort=str2func('@(x,T_set_r,T_room_m,T_room_mm,DT_m,DT_L,DT_U,T_room,Gt,dc,Q_HVAC,N_slot,T_set_w,dT_L,dT_U,Tw_m,Tw_mm,f_t,G,Bt,Rt,dT_m,T_w,T_env,T_n,Q_CHPU)Fcomfort(x,T_set_r,T_room_m,T_room_mm,DT_m,DT_L,DT_U,T_room,Gt,dc,Q_HVAC,N_slot,T_set_w,dT_L,dT_U,Tw_m,Tw_mm,f_t,G,Bt,Rt,dT_m,T_w,T_env,T_n,Q_CHPU)');

but remember that the effect of that would be to index the character vector fcomfort, not execute a function named fcomfort.