You have the assumption that A is incremental. If it is always true, it can be done like this.
%%
A= [ 47 100 153 207 261 314 368 422 474 527 581 635 687 741 794 847 900 954 1007 1060];
B=[301 602 903];
indexA=sum(A'<=B)
indexA =
5 11 17
If A is not always incremental, you could do this. The one thing that you might not have been aware of is called "implict expansion", like C=A'-B in this case. In MATLAB® R2016b and later, you can directly use operators instead of bsxfun(), since the operators independently support implicit expansion of arrays with compatible sizes.
%%
A= [ 47 100 153 207 261 314 368 422 474 527 581 635 687 741 794 847 900 954 1007 1060];
B=[301 602 903];
C=A'-B;
C(C>=0)=nan;
[~,indexA]=max(C)
indexA =
5 11 17
