MATLAB: How to replace any value into vector or matrix to -inf

Question

 ab =
   11.0000
   11.5000
   12.0000
   12.1000
   12.2000
   12.3000
   11.2000
    9.0000
    9.5000
   11.3000
 ab<10
 ans =
Columns 1 through 9
     0     0     0     0     0     0     0     1     1
Column 10
     0
 ab1

ab1 =

Columns 1 through 5
   11.0000   11.5000   12.0000   12.1000   12.2000
   11.1000   11.4000   12.0000   12.1000   12.2000
Columns 6 through 10
   12.3000   11.2000    9.0000    9.5000   11.3000
   12.3000   11.2000    9.0000    9.5000   11.3000

>> ab1<10

ans =

Columns 1 through 9
     0     0     0     0     0     0     0     1     1
     0     0     0     0     0     0     0     1     1
Column 10
     0
     0

i want to replace ab<10 to -inf, without loop, and other variables and matrix size remains same. It should be applicable to any type of matrix.

Answer 1

ab(ab<10) = -inf;