Guide: Determining the Target Code Date from snapshot.diff

July 31, 2026 ยท View on GitHub

When using the parameter upgrade utility util/update_inp.py, you must provide the approximate target date of the GeoFLAC engine version that the old parameter file was written for. If you only have a snapshot.diff (or patch file), this guide explains the two systematic methods to extract the correct code date.

Method 1: The Direct Commit Hash Lookup (Most Precise)

If your snapshot.diff was generated using git diff or git format-patch, the diff headers contain baseline commit hashes.

Step 1: Locate baseline commit hashes in the diff

Open snapshot.diff and look for the file diff index headers:

diff --git a/src/read_params.f90 b/src/read_params.f90
index 5b4b263..c2af4d2 100644
--- a/src/read_params.f90
+++ b/src/read_params.f90

In the index 5b4b263..c2af4d2 line:

  • 5b4b263 is the baseline (old) git commit SHA-1 prefix before changes.
  • c2af4d2 is the new commit SHA-1 prefix.

Step 2: Query git for the commit date

Run the following git command in the repository to extract the commit's calendar date:

git show -s --format=%ad --date=short 5b4b263
  • Expected Output: A date string in YYYY-MM-DD format (e.g., 2026-05-27).
  • Use this exact date string as the second parameter in util/update_inp.py!

Method 2: Syntax-Based Feature Matching (Structural Heuristic)

If the commit hashes are not in your repository (or if snapshot.diff is an ordinary unified diff file without git metadata), you can identify the epoch by looking at which variables are read or written in snapshot.diff and comparing them against our reference mapping:

1. Check the Rheology parameters block

Examine the src/read_params.f90 section of the diff:

  • Has vactiv: If the rheology line reads vactiv (25 parameters), the codebase date is on or after 2025-10-17.
  • Does not have vactiv: If the rheology line does not read vactiv (24 parameters), the codebase date is before 2025-10-17.

2. Check the Thermal parameters block

  • Has extra_pres: If extra_pres is read right after i_prestress, the date is on or after 2025-10-17.
  • Does not have extra_pres: The date is before 2025-10-17.

3. Check the Magma / Melting parameters block

Find the melting lines inside src/read_params.f90 in the diff:

  • Has prod_magma2: If the line has itype_melting, nelem_serp, nelem_dike, prod_magma, prod_magma2, rho_magma (6 values), the date is on or after 2026-07-30.
  • Has nelem_dike but NOT prod_magma2: If the line has itype_melting, nelem_serp, nelem_dike, prod_magma, rho_magma (5 values), the date is between 2026-05-27 and 2026-07-30.
  • Has rho_magma but NOT nelem_dike: If it reads itype_melting, nelem_serp, prod_magma, rho_magma (4 values), the date is between 2023-02-01 and 2026-05-27.
  • Has prod_magma but NOT rho_magma: If it reads itype_melting, nelem_serp, prod_magma (3 values), the date is between 2021-08-10 and 2023-02-01.
  • Has arc_extrusion_rate: The date is before 2021-08-10.

4. Check the nzone_age column format

  • Split 3-Line layout with nph_layer on Line 2: The date is on or after 2023-02-01.
  • Split 3-Line layout with nph_layer on Line 1: The date is between 2023-01-07 and 2023-02-01.
  • Flat 1-Line layout with 15 values (ictherm present): The date is between 2023-01-05 and 2023-01-07.
  • Flat 1-Line layout with 12 values (ictherm absent): The date is before 2023-01-05.

Epoch Quick-Reference Date Summary

Once you match the structural changes, select a date within the identified epoch range:

  • Before 2021-07-15: Pre-tracer removal build.
  • 2021-07-15: Tracer block replaced by dummy lines.
  • 2021-08-10: Chamber max and extrusion rate renamed.
  • 2023-01-05: ictherm added to nzone_age columns.
  • 2023-01-07: nzone_age split into 3-line format.
  • 2023-01-17: Obsolete phase layers and tracer variables removed.
  • 2023-02-01: nph_layer moved to line 2; added rho_magma and latent_heat_magma.
  • 2023-02-04: angle_mzone renamed and simplified.
  • 2025-10-17: Added extra_pres and rheology vactiv parameter.
  • 2026-05-27: Added crustal dike width nelem_dike.
  • 2026-07-30: Added hydrous-mantle magma migration rate prod_magma2.