A matrix with 0 determinant whose determinant becomes nonzero when any element on or below the diagonal is changed from 0 to 1. An example is
There are 
 minimal special matrices of size 
.
 
	    
	
    
A matrix with 0 determinant whose determinant becomes nonzero when any element on or below the diagonal is changed from 0 to 1. An example is
There are 
 minimal special matrices of size 
.
Weisstein, Eric W. "Minimal Matrix." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/MinimalMatrix.html