B.1 Level 1 Subprograms

B.1.1 ALWET

J1FIX (2.1), J1TWER (2.2), STOSIM (3.2), J1BTA (4.2), MLT0PT (4.5),

J1TEAR (5.6), RSTSIM (5.11), SUBSIM (5.12), CLRMEM (6.3), RDDISK (6.16),

SEARCH (6.17), WRTDSK (6.22).

 The subroutine "ALWET" performs the weighted tearing algorithm

 of Pho and Lapidus (1973). ALWET is the executive routine which directs

 the selection of the set of tear variables. It accepts as input an

 output set assigned SIM, with weights assigned to the columns. These

 weights are stored in the sixth word of the C-cells.

 ALWET first calls the subprogram ST0SIM to store the original

SIM. Then it determines whether any of the rows in the SIM have more

than one output. If any do, the subprogram MLT0PT is called to create

a separate row for each output. ALWET sets up a stack of names of SIM's

which are stored in the memory system.

 Next, J1BTA is called to perform the Basic Tearing Algorithm. If

this is successful, the original SIM is restored by RSTSIM, after the

name of the SIM is found by SEARCH. The tear variables are indicated

in the original SIM by the second word of the C-cell being set to 2.

If the BTA fails, the two-way edge reduction subroutine, JiTWER, is

called. If any two-way edges were identified JIBTA is re-applied.

Otherwise J1TEAR is called to choose a tear variable. (This is a

deviation from the Pho and Lapidus algorithm, which would choose the

tear by applying a branch and bound search.)

 As the size of the SIM decreases, rather than continually oper-

ating on the entire SIM, the subprogram SUBSIM is used to eliminate the