Question 13915: One Passing Vector Does Not Certify a Uniform Bound

Original question and givens

Use the explicit rectangular integer matrix A=[[2, -3, 4], [2, -2, -1]] as a linear map between its column- and row-coordinate real spaces. Both ends use the same stated l1 or linfinity norm. A single C≥0 must bound every input: norm(A*x)≤C*norm(x). The exact l1 induced norm is the maximum absolute column sum; the exact linfinity induced norm is the maximum absolute row sum. An instance pass or a nonoptimal usable bound is not the exact operator norm. norm_name=l1, vector=[1, 2, -3], proposed C=7. Give (norm_name,vector,image,input_norm,output_norm,C,rhs=C*input_norm,pass?,instance_only).

• G001 — Use the explicit rectangular integer matrix A=[[2, -3, 4], [2, -2, -1]] as a linear map between its column- and row-coordinate real spaces. Both ends use the same stated l1 or linfinity norm. A single C≥0 must bound every input: norm(A*x)≤C*norm(x). The exact l1 induced norm is the maximum absolute column sum; the exact linfinity induced norm is the maximum absolute row sum. An instance pass or a nonoptimal usable bound is not the exact operator norm. norm_name=l1, vector=[1, 2, -3], proposed C=7. Give (norm_name,vector,image,input_norm,output_norm,C,rhs=C*input_norm,pass?,instance_only).

Definition and scope

Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate.

• mko-bounded-linear-operator

Step-by-step derivation

provided input image:matrix=[[2, -3, 4], [2, -2, -1]];input=[1, 2, -3]

input dimension=3;output dimension=2;rows dot input

provided input image row0 column0 product := mul(2, 1)

provided input image row0 column0 product = 2

provided input image row0 column1 product := mul(-3, 2)

provided input image row0 column1 product = -6

provided input image row0 column2 product := mul(4, -3)

provided input image row0 column2 product = -12

provided input image row0 sum := sum(2, -6, -12)

provided input image row0 sum = -16

provided input image row1 column0 product := mul(2, 1)

provided input image row1 column0 product = 2

provided input image row1 column1 product := mul(-2, 2)

provided input image row1 column1 product = -4

provided input image row1 column2 product := mul(-1, -3)

provided input image row1 column2 product = 3

provided input image row1 sum := sum(2, -4, 3)

provided input image row1 sum = 1

provided input:signed vector=[1, 2, -3];norm=l1

coordinate absolute values=[1, 2, 3]

provided input l1 sum := sum(1, 2, 3)

provided input l1 sum = 6

provided output:signed vector=[-16, 1];norm=l1

coordinate absolute values=[16, 1]

provided output l1 sum := sum(16, 1)

provided output l1 sum = 17

proposed C times input norm := mul(7, 6)

proposed C times input norm = 42

provided input=[1, 2, -3];output norm=17;C=7;input norm=6;rhs=42

this instance passes=Yes;instance_only

Reverse checks

• S015 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
• S014 · premise_and_result_audit — Recompute proposed C times input norm with exact rational arithmetic, not rounded decimals.
• S013 · premise_and_result_audit — Recompute provided output l1 sum with exact rational arithmetic, not rounded decimals.
• S012 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
• S011 · premise_and_result_audit — Recompute provided input l1 sum with exact rational arithmetic, not rounded decimals.
• S010 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
• S009 · premise_and_result_audit — Recompute provided input image row1 sum with exact rational arithmetic, not rounded decimals.
• S008 · premise_and_result_audit — Recompute provided input image row1 column2 product with exact rational arithmetic, not rounded decimals.
• S007 · premise_and_result_audit — Recompute provided input image row1 column1 product with exact rational arithmetic, not rounded decimals.
• S006 · premise_and_result_audit — Recompute provided input image row1 column0 product with exact rational arithmetic, not rounded decimals.
• S005 · premise_and_result_audit — Recompute provided input image row0 sum with exact rational arithmetic, not rounded decimals.
• S004 · premise_and_result_audit — Recompute provided input image row0 column2 product with exact rational arithmetic, not rounded decimals.
• S003 · premise_and_result_audit — Recompute provided input image row0 column1 product with exact rational arithmetic, not rounded decimals.
• S002 · premise_and_result_audit — Recompute provided input image row0 column0 product with exact rational arithmetic, not rounded decimals.
• S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.

Result

(l1, [1, 2, -3], [-16, 1], 6, 17, 7, 42, Yes, instance_only)

The full substitutions and premise checks give the original answer; source identity,format and status are unchanged.

This question review and source binding

Review date: 2026-10-26

Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof.