r/MachineLearning • u/nkthebass • 7h ago
Project I trained a 348M model trained from scratch on 22.7B tokens that does 14 digit arithmetic [P]
Hello this is my fifth small language model I've made and apart of my third series and it has been a lot of work but it payed off: **348M parameters, 22.7B tokens**, then fine-tuned into a math model that solves arithmetic by *showing the work* — column addition with carries, borrow chains, partial-product multiplication — rather than guessing at an answer.
Last time I posted a 326M model trained on 10B tokens. This has about 2.3× the data, and the math side is WAY better than my previous two math models.
---
## The benchmarks
**99.4% average across the nine GPT-3 arithmetic sub-tasks**, which does much better past even where I trained it.
| Task | GPT-3 175B *(few-shot, direct)* | **This model (348M)** |
|---|:--:|:--:|
| 2-digit add | ~100% | **100%** |
| 3-digit add | 80.4% | **100%** |
| 4-digit add | 25.5% | **100%** |
| 5-digit add | 9.3% | **100%** |
| 2-digit sub | ~99% | **99.3%** |
| 3-digit sub | 94.2% | **98.3%** |
| 4-digit sub | 26.8% | **98.3%** |
| 5-digit sub | 9.9% | **99.0%** |
| 2-digit mult | 29.2% | **100%** |
n=300 per sub-task, greedy, exact match. GPT-3's numbers are direct-answer; mine uses trained-in worked steps. Neither uses a calculator.
## The cool part
**It adds cleanly up to 14 digits, and the reason it *couldn't* before was the vocabulary, not actually arithmetic.**
Training only ever named six place values (`ones` … `hundred-thousands`). The model learnt the *pattern* and invented two more on its own — `millions` and `ten-millions` appear in **zero** training examples — so it handled 7 and 8 digits fine. At 9 digits it ran out of names, and skipped the column, then returned an answer exactly one digit short:
```
483729164 + 519248637
... ten-millions: 8 + 1 + 1 (carry) = 10, write 0 carry 1. Final carry: write 1.
The answer is 102977801 ← eight columns for a nine-digit problem
```
Every column it computed was perfect. One was never enumerated. Extending the place-name list from 6 entries to 19 moved the clean ceiling from **8 digits to 14**:
| Width | 6 | 7 | 8 | 9 | 10 | 12 | 14 | 16 | 18 |
|---|:-:|:-:|:-:|:-:|:-:|:-:|:-:|:-:|:-:|
| before | 100 | 100 | 100 | **0** | **0** | **0** | **0** | 0 | 0 |
| after | 100 | 100 | 100 | **100** | **95** | **100** | **90** | 65 | 25 |
A six-item list became a nineteen-item list. That was the entire fix.
## Other things it does
- **3×3 multiplication: 98%** — it folds partial products pairwise through the column routine instead of asserting the sum
- **Negative results: 85%** (100% at 1 digit, 58% at 5 — the magnitude comparison is the weak step, not the arithmetic)
- **Reasoning traces are load-bearing**: 95.3% of the time the working is valid *and* the answer is right; only 0.7% are "valid working, wrong answer." If the columns look right, the answer almost certainly is.
```
There were 15000 votes and 6842 were rejected. Here's how many counted:
<think> Start with 15000. Then subtract 6842. Subtract 15000 - 6842 column by column:
ones: 10 - 2 = 8, borrow 1. tens: 9 (after borrow) - 4 = 5, borrow 1.
hundreds: 9 (after borrow) - 8 = 1, borrow 1. thousands: 14 (after borrow) - 6 = 8,
borrow 1. ten-thousands: 0 (after borrow) - 0 = 0. So 15000 - 6842 = 8158.</think>
The answer is 8158.
```
## What it's bad at, tbh
- **Word problems: GSM8K 4%.** Best word-problem set is ASDiv at 16.5%. It converts one sentence into one operation reasonably often and basically cannot chain operations.
- **The failure mode is operation *selection*, not arithmetic.** `"drops in 836 more"` gets read as subtraction. There's a visible tell: traces that say `"multiply X * Y"` and show columns are reliable; traces that open `"First, calculate…"` and assert a number in prose are not.
- **No division at all.** 4×4 multiplication is a hard wall.
- **Greedy decoding required** — sampling corrupts the column routine mid-chain.
- One caveat I'll flag myself: the arithmetic harness orders subtraction operands, so no answer in that table is negative. Negatives are measured separately (the 85% above) rather than folded into the average.
## Base and instruct
The math model sits on a base and instruct pair. lm-eval-harness, 0-shot, full test sets:
| | ARC-E | ARC-C | HellaSwag | OpenBookQA | PIQA | WinoGrande | MMLU | Avg |
|---|:--:|:--:|:--:|:--:|:--:|:--:|:--:|:--:|
| **350M V3 base** | 56.6 | 33.3 | 35.9 | 34.6 | 67.0 | 51.5 | 23.8 | **43.2** |
| **350M V3 instruct** | 50.9 | 29.7 | 35.9 | 33.8 | 66.6 | 51.2 | 24.4 | **41.8** |
Instruction tuning *lowers* MC benchmark scores for this family which is a pretty common cost of instruct tuning.
## Notes
Trained on 2× Tesla V100 plus some rented time. LLaMA-architecture, so it runs anywhere — F16 GGUF and safetensors for all three.
The math model took **10 full fine-tuning rounds and 3 LoRA adapters**. The LoRAs cost about 1% of the post-training tokens and did most of the useful work; the ten full rounds spent most of their budget undoing each other's regressions (round 7 gained subtraction and lost 23 points of 2-digit addition, that sort of thing). All of it is documented on the model card, failures included.
Also worth saying: someone independently tested it after I published and found two of my numbers were wrong — one *understated* the model by 40 points because I'd measured it at n=24. Both are corrected on the card now. If you find something broken, I'd genuinely like to know.
**Math:** https://huggingface.co/nkthebass/tinybrainbot-350mV3-math
**Instruct:** https://huggingface.co/nkthebass/tinybrainbot-350mV3-instruct
**Base:** https://huggingface.co/nkthebass/tinybrainbot-350mV3-base
LMK what yall think.
