Linear Congruence order 4 sequence not testing in PFGW?

[CRGreathouse]

I would track the index, incrementing by 1 each time. Then when you come to output, either output only the index, or else output the index followed by the full number.

I would also remove prime_file (in both places) since you don't seem to use it.

[rogue]

Is it possible for an to go negative? If not, but it is in code, then you have problem.

[paulunderwood]

this tests for negative "an":

SCRIPT

DIM anm1, 8
DIM anm2, 7
DIM anm3, 4
DIM anm4, 1
DIM anmin, 2^1
DIM anmax, 2^300000
DIM an
DIM abs_an
DIM index_n, 4

OPENFILEAPP prp_file,prp.txt

LABEL start
SET an,4*anm1-7*anm2+8*anm3-4*anm4

IF (an<0) THEN SET abs_an,-an ELSE SET abs_an,an

IF (abs_an<anmin) THEN GOTO next_iteration
IF (abs_an>anmax) THEN GOTO the_end

FACTORIZE index_n
IF (ISPRIME) THEN GOSUB test

LABEL next_iteration
SET anm4, anm3
SET anm3, anm2
SET anm2, anm1
SET anm1, an
SET index_n, index_n+1
GOTO start

LABEL test
PRP abs_an
IF (ISPRP) THEN WRITE prp_file,index_n
RETURN

LABEL the_end
CLOSEFILE prp_file
END

[carpetpool]

Originally Posted by paulunderwood

this tests for negative "an":

SCRIPT

DIM anm1, 8
DIM anm2, 7
DIM anm3, 4
DIM anm4, 1
DIM anmin, 2^1
DIM anmax, 2^300000
DIM an
DIM abs_an
DIM index_n, 4

OPENFILEAPP prp_file,prp.txt

LABEL start
SET an,4*anm1-7*anm2+8*anm3-4*anm4

IF (an<0) THEN SET abs_an,-an ELSE SET abs_an,an

IF (abs_an<anmin) THEN GOTO next_iteration
IF (abs_an>anmax) THEN GOTO the_end

FACTORIZE index_n
IF (ISPRIME) THEN GOSUB test

LABEL next_iteration
SET anm4, anm3
SET anm3, anm2
SET anm2, anm1
SET anm1, an
SET index_n, index_n+1
GOTO start

LABEL test
PRP abs_an
IF (ISPRP) THEN WRITE prp_file,index_n
RETURN

LABEL the_end
CLOSEFILE prp_file
END

The code seems to work in general, that's good. I tried to set the odd values of the initial sequence negative, and for some reason only tested the even values. Either that, or I had the index off by 1.

SCRIPT

DIM anm1, 8
DIM anm2, -7
DIM anm3, 4
DIM anm4, 1
DIM anmin, 2^1
DIM anmax, 2^300000
DIM an
DIM abs_an
DIM index_n, 4

OPENFILEAPP prp_file,prp.txt

LABEL start
SET an,-4*anm1-7*anm2-8*anm3-4*anm4

IF (an<0) THEN SET abs_an,-an ELSE SET abs_an,an

IF (abs_an<anmin) THEN GOTO next_iteration
IF (abs_an>anmax) THEN GOTO the_end

FACTORIZE index_n
IF (ISPRIME) THEN GOSUB test

LABEL next_iteration
SET anm4, anm3
SET anm3, anm2
SET anm2, anm1
SET anm1, an
SET index_n, index_n+1
GOTO start

LABEL test
PRP abs_an
IF (ISPRP) THEN WRITE prp_file,index_n
RETURN

LABEL the_end
CLOSEFILE prp_file
END