Maximum value in a vector

Problem statement: Use the max function to find the value and location of the maximum y value. Use fprintf to show the maximum y and the x value for which it occurs. When I use the max function it always returns -1?

x = [linspace(-pi,pi,10)]
n = [length(x)];
for i = 1:n
    fprintf(' %.0f: %f  ', i, x(i))
end
for i = 1:n
    y = [cos(x(i))];
    fprintf(' %f ',y)
end
max(y)

Answer 1

[Stephen23]

The problem is that you don't have a vector, although you think that you do. Actually y is a scalar value -1, so of course min(-1) will give you that output. This happens because you simply reallocate y on every loop iteration, so at the end of the loop it only has the last value. You could use indexing to fix this.

A much better way to solve this problem is entirely without loops:

>> X = linspace(-pi,pi,10);
>> Y = cos(X);
>> [maxY,idx] = max(Y);
>> maxX = X(idx)
maxX = -0.34907
>> maxY
maxY =  0.93969

Loops are often an inefficient way of solving problems in MATLAB.

[NT]

The instructions of the program told us to do the y value in a for loop, so is there anyway to find the max using the max functions while still keeping the for loop?

[Stephen23]

Like I said: use indexing to store the y values in the loop. Then apply max after the loop. Indexing is covered in thousand of tutorials online, so you won't have any problem with that.

[sunil shetty]

Hi ,

Is this solution applicable for 2D or 3D vector ?

Thanks & Regards ,

Sunil