p?lacon

Estimates the 1-norm of a square matrix, using the reverse communication for evaluating matrix-vector products.

Syntax

call pslacon(n, v, iv, jv, descv, x, ix, jx, descx, isgn, est, kase)

call pdlacon(n, v, iv, jv, descv, x, ix, jx, descx, isgn, est, kase)

call pclacon(n, v, iv, jv, descv, x, ix, jx, descx, isgn, est, kase)

call pzlacon(n, v, iv, jv, descv, x, ix, jx, descx, isgn, est, kase)

Description

The p?lacon routine estimates the 1-norm of a square, real/unitary distributed matrix A. Reverse communication is used for evaluating matrix-vector products. x and v are aligned with the distributed matrix A, this information is implicitly contained within iv, ix, descv, and descx.

Input Parameters

n

(global) INTEGER. The length of the distributed vectors v and x. n 0.

v

(local).

REAL for pslacon

DOUBLE PRECISION for pdlacon

COMPLEX for pclacon

COMPLEX*16 for pzlacon.

Pointer into the local memory to an array of size LOCr(n+mod(iv-1, mb_v)). On the final return, v = a*w, where est = norm(v)/norm(w) (w is not returned).

iv, jv

(global) INTEGER. The row and column indices in the global matrix V indicating the first row and the first column of the submatrix V, respectively.

descv

(global and local) INTEGER array of size dlen_. The array descriptor for the distributed matrix V.

x

(local).

REAL for pslacon

DOUBLE PRECISION for pdlacon

COMPLEX for pclacon

COMPLEX*16 for pzlacon.

Pointer into the local memory to an array of size LOCr(n+mod(ix-1, mb_x)).

ix, jx

(global) INTEGER. The row and column indices in the global matrix X indicating the first row and the first column of the submatrix X, respectively.

descx

(global and local) INTEGER array of size dlen_. The array descriptor for the distributed matrix X.

isgn

(local). INTEGER.

Array of size LOCr(n+mod(ix-1, mb_x)). isgn is aligned with x and v.

kase

(local). INTEGER.

On the initial call to p?lacon, kase should be 0.

Output Parameters

x

(local).

On an intermediate return, X should be overwritten by A*X, if kase=1, A' *X, if kase=2,

p?lacon must be re-called with all the other parameters unchanged.

est

(global). REAL for single precision flavors

DOUBLE PRECISION for double precision flavors

kase

(local)

INTEGER. On an intermediate return, kase is 1 or 2, indicating whether X should be overwritten by A*X, or A'*X. On the final return from p?lacon, kase is again 0.

See Also

For more complete information about compiler optimizations, see our Optimization Notice.