let n be Nat; for M1, M2 being Matrix of n,REAL st M1 is Nonpositive & M2 is Nonpositive holds
M1 + M2 is Nonpositive
let M1, M2 be Matrix of n,REAL; ( M1 is Nonpositive & M2 is Nonpositive implies M1 + M2 is Nonpositive )
assume that
A1:
M1 is Nonpositive
and
A2:
M2 is Nonpositive
; M1 + M2 is Nonpositive
A3:
Indices M1 = [:(Seg n),(Seg n):]
by MATRIX_0:24;
A4:
Indices (M1 + M2) = [:(Seg n),(Seg n):]
by MATRIX_0:24;
A5:
Indices M2 = [:(Seg n),(Seg n):]
by MATRIX_0:24;
for i, j being Nat st [i,j] in Indices (M1 + M2) holds
(M1 + M2) * (i,j) <= 0
proof
let i,
j be
Nat;
( [i,j] in Indices (M1 + M2) implies (M1 + M2) * (i,j) <= 0 )
assume A6:
[i,j] in Indices (M1 + M2)
;
(M1 + M2) * (i,j) <= 0
then
M1 * (
i,
j)
<= 0
by A1, A3, A4;
then A7:
(M1 * (i,j)) + (M2 * (i,j)) <= M2 * (
i,
j)
by XREAL_1:32;
M2 * (
i,
j)
<= 0
by A2, A5, A4, A6;
hence
(M1 + M2) * (
i,
j)
<= 0
by A3, A4, A6, A7, MATRIXR1:25;
verum
end;
hence
M1 + M2 is Nonpositive
; verum