Can someone please tell why I have an error?

[Abdulrahman Al Ali]

fa=@(x) (2.*x.^3+3.*x.^2-6.*x+19)./(7.*x.^3-20.*x-5);  % define the function for part (a)-REMEMBER to use element-by-element operations (.*  ./  .^)
x=[-10 -100 -1000 -10000]; % define the vector x
for i=1:4
    disp(fa(x(i))); 
end    % calculate f(x) (No semicolon to see output)
syms x; % DO NOT CHANGE CODE ON THIS LINE
aLimit=limit(fa(x),x,Inf)  % No semicolon
disp('2/7=0.2857')




% Repeat the above process for part (b)
fa=@(x) sqrt(4*x^2+7*x+1)-2*x; 
x=[-10 -100 -1000 -10000];
for i=1:4
    disp(fa(x(i))); 
end    
syms x;
bLimit=limit(fa(x),x,Inf)
disp(7/4)

[Adam Danz]

Somewhere in your code you are execting a line that contains a variable or function named "ya" and matlab doens't know what it is because it's not defined. But "ya" isn't in the code you shared so it must happen elsewhere in your code.

[Abdulrahman Al Ali]

so, should i rewrite ’ya’ ? ... i tried to write ”ya” in many different ways but, I seem to get error every time. what would you advise me?

[Adam Danz]

No, adding "ya" somewhere in your code isn't the solution.

Here's what I suggest: provide all of the code by copy and pasting (not by sharing a screen shot) and then provide the full error message (again, no screen shots unless they are super clear and easy to read).

[Abdulrahman Al Ali]

The instruction I was given as follow not including the limits equations:

1. Define the function f as an anonymous function using element-by-element operations.
2. Estimate the limit by defining x=[10 100 1000 10000] (or use negative values if x approaches negative infinity) and calculate f(x).
3. Redefine x as a symbolic variable and find the limit of f(x) symbolically using the limit command.

My code:

fa=@(x) (2.*x.^3+3.*x.^2-6.*x+19)./(7.*x.^3-20.*x-5);  % define the function for part (a)-REMEMBER to use element-by-element operations (.*  ./  .^)
x=[-10 -100 -1000 -10000]; % define the vector x
ya= 0.2857 % calculate f(x) (No semicolon to see output)
syms x; % DO NOT CHANGE CODE ON THIS LINE
aLimit=limit(fa(x),x,Inf)  % No semicolon
assert(isequal(double(aLimit),2/7)),


% Repeat the above process for part (b)
fb=@(x) sqrt(4.*x.^2+7.*x+1)-2.*x; 
x=[10 100 1000 10000];
yb= 1.7499
syms x;
bLimit=limit(fb(x),x,Inf)
assert(isequal(double(bLimit),7/4)),

The error messages:

1- X Test values of ya

Student code gives incorrect y-values for part (a)

2- X Test values of yb

Student code gives incorrect y-values for part (b)

[Walter Roberson]

Your code does not calculate y.

We have not seen the assignment so we do not know exactly what needs to be calculated.

[Abdulrahman Al Ali]

[Walter Roberson]

You are not calculate f() at each of those numeric x values.

[Abdulrahman Al Ali]

I don’t really get it but, thanks anyway!!

Answer 1

[madhan ravi]

Instead of line (this is what sir Walter mentioned in the above) :

ya=f(x) %change your lines to these lines 
yb=f(x)