How to find minimum value from loop using if function iteration?

I have a=6.5, I would like to define "if function" inside the "for loop", for i=1:10, it will do the loop imin < a < imax, and if the "if function" is correct, I would like to use the b= imin (in which the a function is correct).

My expectation toward the code is b=6. Since the 6.5 is in between number for loop 6 and 7. And I want to use 6 (imin where the a is in correct statemen for if function)

How do I code that in matlab?

a=6.5;
for i=1:10
    imin=i;
    imax=imin+1
    if imin<a<imax
        b=imin;
    end
    if imax==10;
    end
end

[Stephen23]

https://www.mathworks.com/help/matlab/ref/floor.html

[Anom Sulardi]

Hi Stephen,

Thank you for the answer. But, how if in the case of hundred thousand. I can not use floor() function for it. Otherwise, I still need to use if function inside for loop, if it is possible?

For example:

From below code, I expect to have b value in 135, since a is between 135000 and 136000. and b=imin/dx=135.

a=135500;
dx=1000;
for i=1:10
    imin=i*dx;
    imax=imin+dx
    if imin<a<imax
        b=imin/dx;
    end
    if imax==10;
    end
end

Answer 1

[Stephen23]

>> a = 135500;
>> dx = 1000;
>> b = floor(a/dx)
b =  135

[Stephen23]

Anom Sulardi's "Answer" moved here:

Hi Stephen,

Thanks again for your kind help. In some cases, I can use that code actually.

So, this is my actual code now.

I expect to have result KK=3 since z0 is in between the hh(3)=9.5 and hh(4)=16. That's why I prefer to use if function inside for looping.

hh=[1.5, 5, 9.5, 16, 25, 37.5, 57.5, 95, 160, 250, 400, 600, 850, 1250, 2250];
z0=11.5;
for k=1:15 % I have 15 layer of hh
    if hh(k)<=z0<hh(k+1)
        KK=k % please do find KK= minimum k where statement is true
    end
end

[Stephen23]

>> hh = [1.5, 5, 9.5, 16, 25, 37.5, 57.5, 95, 160, 250, 400, 600, 850, 1250, 2250];
>> z0 = 11.5;
>> KK = find(hh<=z0,1,'last')
KK =   3

[Anom Sulardi]

Hi Stephen,

Thank you so much. That's really help me a lot.

However, I have another problem. How can I indexing 4-D array matrix by using 2-d or 3-d array?

Let say, I want to index the 4-D matrix A with the A(3,5,7,10) and A(4,6,8,10). However, the first, second, and third array on indexing is exist inside the matrix a,b,c. Can matlab do this?

I try to use diag(C), but it doesn't work well.

A=rand(10,10,10,10);
a=[3;4];b=[5,6];c=[7,8];

C=A(a,b,c,10);

[Stephen23]

Use sub2ind:

A = rand(10,10,10,10);
a = [3,4];
b = [5,6];
c = [7,8];
X = sub2ind(size(A),a,b,c,[10,10]);
C = A(X)

Answer 2

[bharath pro]

Instead of using imin<a<imax, try using an intersection of two commands for checking less than and greater than seperatly.

a=6.5;
for i=1:10
    imin=i;
    imax=imin+1
    if (imin<a)&&(a<imax)
        b=imin;
    end
    if imax==10;
    end
end

This will give the output as 6

[Anom Sulardi]

thank you, it works really well.