let n be Nat; :: thesis: for M being Matrix of n, REAL st M is Nonpositive holds
- M is Nonnegative
let M be Matrix of n, REAL ; :: thesis: ( M is Nonpositive implies - M is Nonnegative )
A1: ( Indices M = [:(Seg n),(Seg n):] & Indices (- M) = [:(Seg n),(Seg n):] ) by MATRIX_1:25;
assume A2: M is Nonpositive ; :: thesis: - M is Nonnegative
for i, j being Nat st [i,j] in Indices (- M) holds
(- M) * i,j >= 0

proof

let i, j be Nat; :: thesis: ( [i,j] in Indices (- M) implies (- M) * i,j >= 0 )
assume A3: [i,j] in Indices (- M) ; :: thesis: (- M) * i,j >= 0
then M * i,j <= 0 by A2, A1, Def3;
then - (M * i,j) >= 0 ;
hence (- M) * i,j >= 0 by A1, A3, Th2; :: thesis: verum

end;

hence - M is Nonnegative by Def4; :: thesis: verum