E-CodeLU decomposition with partial pivoting — a TI-84 Plus CE program
LUDECOMP is a TI-BASIC program for the TI-84 Plus CE. Factor a 2×2 to 4×4 matrix as PA = LU with partial pivoting: every entry of L and U, the row order P and the determinant.
What it asks for and what it shows
It asks for 4 values at its prompts. In the example below it shows L11, L12, L13, L21, L22, L23, L31, L32, L33, U11, U12, U13, U21, U22, U23, U31, U32, U33, DET, P1=ROW, P2=ROW, P3=ROW.
Example run
One of its oracle test cases: “3x3 with a row swap”. The inputs are typed in order, and the results are the values the case expects on the screen.
| Step | Value |
|---|---|
| You enter | |
| Input 1 | 3 |
| Input 2 | {2,1,1} |
| Input 3 | {4,⁻6,0} |
| Input 4 | {⁻2,7,2} |
| The screen shows | |
L11= | 1 |
L12= | 0 |
L13= | 0 |
L21= | 0.5 |
L22= | 1 |
L23= | 0 |
L31= | -0.5 |
L32= | 1 |
L33= | 1 |
U11= | 4 |
U12= | -6 |
U13= | 0 |
U21= | 0 |
U22= | 4 |
U23= | 1 |
U31= | 0 |
U32= | 0 |
U33= | 1 |
DET= | -16 |
P1=ROW | 2 |
P2=ROW | 1 |
P3=ROW | 3 |
How it's checked
4 test cases, each checked against an independent method. Replayed key by key on a virtual TI-84 Plus CE, they make 79 checks.
How E-Code checks every program
Run it or put it on your calculator
- Open the library in the TI-84 Plus CE calculator and pick “LU decomposition with partial pivoting” (LUDECOMP).
- Put it on your own calculator with a computer and a USB cable, or type it in by hand.
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All TI-84 Plus CE math programs · All TI-84 Plus CE programs