How do I find a value in a vector using the bisection method?

I'm asked to find the location of the value 25 in a 200 value vector that is in ascending order using the bisection method. So far I have this:

xl=1;
xr=200;
xc=100;
for(j=1:100)
    xc=(xl+xr)/2;
    floor(xc);
    fc=(25-xc);
    if(fc<0)
        xr=xc;
    else
        xl=xc;
    end
    if abs(fc)==0
        break
    end
end
fc
xc
j

And it spits out 0, 25, and 55 for fc, xc, and j respectively.

I'm pretty sure my code is wrong, so I need help on that, but also once I get it right how do I describe the location?

Answer 1

[Walter Roberson]

Your code is not finding the location that contains 25, your code is looking for index 25. Your checking should not be against xc, your checking should be against the vector indexed at floor(fc)

[Brady Retzlaff]

so how do i specify in the code that i am looking for the location that contains 25?

[Walter Roberson]

    xcidx = floor(xc);
    fc = 25 - YourVectorOf200Elements(xcidx);

Answer 2

[Eng. Fredius Magige]

Hi

the uses of

xl=1;
xr=200;
xc=100;

not observed in for(j=1:100) applicability as varies 1:1:100; and intentional use; I though sometning left, might be xr or xc as to varies as j added or substracted. Note from you explanation could be new=xr+(xr+xc)/2

thanks

[Brady Retzlaff]

i dont understand this at all...

[Walter Roberson]

I do not understand it either.