I have this lab I am trying to complete, it is Coding in MATLAB. I was curious how to fix an error I keep receiving.

%%%Error%%%

Error using sym/subsindex (line 853)

Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function

arguments must be symbolic variables, and function body must be sym expression.

Error in Lab9Math2130ahalvors (line 11)

%%% Code %%%

f(x,y)= k*y;

num= 0970974;%student number

k= num/1000000;

syms y;

syms x;

f(x,y)= k*y;

x0= 0;

y0= 1;

h= 0.05;

x= x0;

y= y0;

t= 2;

while x<= t%euler's method

y= y+h*double(f(x,y));

x= x+h;

end

eulerY= y

x= x0;

y= y0;

while x<= t%midpoint method

k1= h*double(f(x ,y));

k2= h*double(f(x+0.5*h, y+0.5*k1));

y= y+k2;

x= x+h;

end

midpointY= y

x= 2;

realY= exp(k*x)%solution to the diffrential eq

RErrorEulers= abs(realY-eulerY)/realY

RErrorMidpoint= abs(realY-midpointY)/realY