invalid use of operator

>>shitathatsia = @(x) 2.7*cos(25*x^2+8*x)-10*x*sin(6*x)

starrt=-1

ennd=1

pitaron= (starrt+ennd)/2

while sqrt((shitathatsia(pitaron))^2)> 0.001

if(shitathatsia(pitaron)) * shitathatsia(start) <0

starrt = pitaron

if shitathatsia(pitaron)) * shitathatsia(start) >0

ennd=pitaron

end

pitaron=(starrt+ennd)/2

end

fprintf(pitaron)

Answer 1

[James Tursa]

You are missing a ( after the second "if", and you are missing an "end" statement. That being said, my suggestion would be to use an "else" instead as that appears to be your intent. E.g.,

if ( condition )
    starrt = pitaron;
else
    ennd = pitaron;
end

[mohammad massarwe]

but i get an error in first line

invalid use of operator

[James Tursa]

Please show your current code with your attempted fixes. And please post your code as text highlighted with the CODE button, not as images. We can't copy & run images at our end.

[mohammad massarwe]

>>shitathatsia = @(x) 2.7*cos(25*x^2+8*x)-10*x*sin(6*x)
starrt=-1
ennd=1
pitaron= (starrt+ennd)/2 
while sqrt((shitathatsia(pitaron))^2)> 0.001
    if(shitathatsia(pitaron)) * shitathatsia(start) <0
        starrt = pitaron
    if shitathatsia(pitaron)) * shitathatsia(start) >0
        ennd=pitaron
    end
    pitaron=(starrt+ennd)/2
    
 end
   
 fprintf(pitaron)

[Walter Roberson]

The >> should not be part of your code

[James Tursa]

This looks like your original code. Why haven't you implemented the fix I suggested? Also, you should be using the variable name starrt instead of start. E.g.,

    if(shitathatsia(pitaron)) * shitathatsia(starrt) <0
        starrt = pitaron;
    else
        ennd = pitaron;
    end    

And it seems like this expression

    sqrt((shitathatsia(pitaron))^2)

could simply be replaced with this

    abs(shitathatsia(pitaron))

[mohammad massarwe]

i have to error from the first line my friend

[mohammad massarwe]

File: untitled.m Line: 1 Column: 1

Invalid use of operator.

[James Tursa]

Get rid of the >> as Walter suggests.

Answer 2

[Abdul-Hamid Mohammed]

for i=1:length(t)-1
    x(i+1)=x(i)+(a*(x^2)(i)*(1+B(x^2)(i)-q*x(i)*E(i)))*Dt;
    E(i+1)=E(i)+(z*(p*q*x(i)*E(i)-c*E(i)))*Dt;
end;

I am getting invalid use of operator with the above syntex, pls how do i resolve it. thank you.

[Walter Roberson]

(x^2)(i)

that would be considered a request to apply a matrix square to x and then index the result at i.

This has two problems:

• matlab does not permit () indexing of the results of a calculation
• your x is a vector but you are taking matrix square, which can only be applied to square matrices, not to vectors.

x^2 is x*x which is inner product of x with itself, also known as matrix multiplication.

Perhaps in your situation it would be acceptable to use x(i).^2

[Abdul-Hamid Mohammed]

Thanks so much for the response. I just tried that option but I'm still getting the same error message

[Abdul-Hamid Mohammed]

% Euler's Method
% Initial conditions and setup
% x(t+1)=x(t)+(a*(x(t)^2)*(1+B(x(t)^2)-q*x(t)*E(t)))*Dt
% E(t+1)=E(t)+(z*(p*q*x(t)*E(t)-c*E(t)))*Dt
%
%=======================================================================
a=1; alpha value
B=25; beta value
q=0.1; %catchability
z=0.1; %effort
p=100; %price
c=4; %cost
Dt=0.01; %delta t
timesteps=50;
t=0.1:Dt:timesteps; %array with time

for i=1:length(t)-1
    x(i+1)=x(i)+(a*(x(i)^2)*(1+B(x(i)^2)-q*x(i)*E(i)))*Dt;
    E(i+1)=E(i)+(z*(p*q*x(i)*E(i)-c*E(i)))*Dt;
end;

[Walter Roberson]

B(x(i)^2) is a request to index your scalar value B at the location determined by the calculation. Perhaps you forgot a multiplication.