Why am I getting an error that matrices must agree?

Working on this question about a Fence problem(Have to write a script about it) and here is my script:

prompt= 'State the Area: ';
Area = input(prompt,'s');
prompt= 'State the Straight Cost: ';
StrCo = input(prompt,'s');
prompt= 'State the Curved Cost: ';
CurCo = input(prompt,'s');

R = .01:.01:sqrt(2*Area/pi);

L = (Area - 1/2*pi*R.^2)/(2*R);

Cost = (2*L+ 2*R)*StrCo +pi*R*CurCo;

[BestCost,Index] = min(Cost);

BestR = R(Index);

BestL = L(Index);

disp(['The best cost is',num2str(min(Cost)),'.'])
disp(['The best radius is',num2str(BestR),'.'])
disp(['The best length is',num2str(BestL),'.'])

But when I go and run my script, I am so confused on why I get this error:

>> untitled3
State the Area: 1600
State the Straight Cost: 30
State the Curved Cost: 40
Error using  - 
Matrix dimensions must agree.

Error in untitled3 (line 10)
L = (Area - 1/2*pi*R.^2)/(2*R);

[Stephen23]

See also original question:

https://www.mathworks.com/matlabcentral/answers/385357-i-need-help-with-using-the-input-function

Answer 1

[Rik]

The documentation states the following

str = input(prompt,'s') returns the entered text, without evaluating the input as an expression.

So your problem is that Area is still a char vector. You need to include the following line of code, just after input to convert the user response to an actual value.

Area=str2double(Area);

Edit: I see Torsten and Andrei have noticed another problem with this line of code: because R is a vector, the division must be element-wise as well.

prompt= 'State the Area: ';
Area = input(prompt,'s');
Area=str2double(Area);
prompt= 'State the Straight Cost: ';
StrCo = input(prompt,'s');
StrCo=str2double(StrCo);
prompt= 'State the Curved Cost: ';
CurCo = input(prompt,'s');
CurCo=str2double(CurCo);
R = .01:.01:sqrt(2*Area/pi);
L = (Area - 1/2*pi*R.^2)./(2*R);
Cost = (2*L+ 2*R)*StrCo +pi*R*CurCo;
[BestCost,Index] = min(Cost);
BestR = R(Index);
BestL = L(Index);
disp(['The best cost is',num2str(min(Cost)),'.'])
disp(['The best radius is',num2str(BestR),'.'])
disp(['The best length is',num2str(BestL),'.'])

[T.Y. Hilton]

The str2double function helped! My code went thought perfectly no problem thank you so much!!

[Stephen23]

@Travis Ward: you got the advice to use str2double eight hours ago:

https://www.mathworks.com/matlabcentral/answers/385357-i-need-help-with-using-the-input-function#answer_307563

Answer 2

[Torsten]

L = (Area - 1/2*pi*R.^2)./(2*R);

Best wishes

Torsten.

Answer 3

[Andrei Bobrov]

prompt= 'State the Area: ';
Area = input(prompt);
prompt= 'State the Straight Cost: ';
StrCo = input(prompt);
prompt= 'State the Curved Cost: ';
CurCo = input(prompt);

R = .01:.01:sqrt(2*Area/pi);

L = (Area - 1/2*pi*R.^2)./(2*R);

Cost = (2*L+ 2*R)*StrCo +pi*R*CurCo;

[BestCost,Index] = min(Cost);

BestR = R(Index);

BestL = L(Index);

disp(['The best cost is ',num2str(min(Cost)),'.'])
disp(['The best radius is ',num2str(BestR),'.'])
disp(['The best length is ',num2str(BestL),'.'])