Add Options reference section

README.md

@@ -6,22 +6,333 @@
 ## License
 
 Please note that go-mip is provided as _source-available_ software (not
-_open-source_). For further information, please refer to the [LICENSE](./LICENSE.md)
-file.
+_open-source_). For further information, please refer to the
+[LICENSE](./LICENSE.md) file.
 
 ## Usage
 
 This library contains the types and interfaces to model and solve MIP problems.
 The implementation is provided by other (solver-specific) packages, e.g.:
 [go-highs](https://github.com/nextmv-io/go-highs).
 
-For further information on how to get started with MIP modeling and Nextmv,
-please refer to the [official documentation](https://docs.nextmv.io/docs/mixed-integer-programming).
+These are the supported solvers and solver interfaces for MIP:
 
-## Versioning
+| Provider | Description |
+| -------- | ----------- |
+| [FICO Xpress][fico-xpress-section] | Commercial solver. |
+| [HiGHS][highs-section] | Open-source solver.  |
+| [OR-Tools][ortools-section] | Open-source solver interface for various solvers. Included open-source solvers: `CLP`, `GLOP`, `PDLP`, `SCIP`. |
+| [Pyomo][pyomo-section] | Open-source interface for various solvers. Included open-source solvers in Cloud: `CBC`, `GLPK`. |
 
-We try our best to version our software thoughtfully and only break APIs and
-behaviors when we have a good reason to.
+More information on supported solvers and solver interfaces is available in the
+[Integrations section of Nextmv Docs][nextmv-docs-integrations].
 
-- Minor (`v1.^.0`) tags: new features, might be breaking.
-- Patch (`v1.0.^`) tags: bug fixes.
+## Options
+
+All MIP applications are configurable through options.
+
+* Runner options change how the runner outputs solutions and reads/writes data.
+* Solve options change the behavior of the solver.
+
+Options can be configured when running locally with the Nextmv CLI or when
+running remotely on Nextmv Platform. Running remotely is possible with a custom
+app or an app subscribed to a Marketplace app. Learn more about [Nextmv
+apps][nextmv-docs-apps].
+
+Note that if both an environment variable and its corresponding CLI flag are
+defined, the CLI flag will overwrite the environment variable.
+
+These are the default options that are available with MIP:
+
+* `-runner.input.path` string
+  * The input file path (env `RUNNER_INPUT_PATH`).
+* `-runner.output.path` string
+  * The output file path (env `RUNNER_OUTPUT_PATH`).
+* `-runner.output.solutions` string
+  * {all, last} (env `RUNNER_OUTPUT_SOLUTIONS`) (default "last").
+* `-runner.profile.cpu` string
+  * The CPU profile file path (env `RUNNER_PROFILE_CPU`).
+* `-runner.profile.memory` string
+  * The memory profile file path (env `RUNNER_PROFILE_MEMORY`).
+* `-solve.control.bool` string
+  * List of solver-specific control options (configurations) with bool values
+    (env `SOLVE_CONTROL_BOOL`). Example: "name1=value1,name2=value2", where
+    value1 and value2 are bool values.
+* `-solve.control.float` string
+  * List of solver-specific control options (configurations) with float values
+    (env `SOLVE_CONTROL_FLOAT`). Example: "name1=value1,name2=value2", where
+    value1 and value2 are float values.
+* `-solve.control.int` string
+  * List of solver-specific control options (configurations) with int values
+    (env `SOLVE_CONTROL_INT`). Example: "name1=value1,name2=value2", where
+    value1 and value2 are int values.
+* `-solve.control.string` string
+  * List of solver-specific control options (configurations) with string values
+    (env `SOLVE_CONTROL_STRING`). Example: "name1=value1,name2=value2", where
+    value1 and value2 are string values.
+* `-solve.duration` duration
+  * Maximum duration of the solver (env `SOLVE_DURATION`) (default 30s).
+* `-solve.mip.gap.absolute` float
+  * Absolute gap stopping value. If the problem is an integer problem the solver
+    will stop if the gap between the relaxed problem and the best found integer
+    problem is less than this value (env `SOLVE_MIP_GAP_ABSOLUTE`) (default
+    1e-06).
+* `-solve.mip.gap.relative` float
+  * Relative gap stopping value. If the problem is an integer problem the solver
+    will stop if the relative gap between the relaxed problem and the best found
+    integer problem is less than this value (env `SOLVE_MIP_GAP_RELATIVE`)
+    (default 0.0001).
+* `-solve.verbosity` value
+  * {off, low, medium, high} Verbosity of the solver in the console (env
+    `SOLVE_VERBOSITY`).
+
+Valid time units for `-solve.duration` are as follows, according to
+[`time.ParseDuration` from Go's standard library][go-parse-duration]:
+
+* `ns` (nanoseconds)
+* `us/µs` (microseconds)
+* `ms` (milliseconds)
+* `s` (seconds)
+* `m` (minutes)
+* `h` (hours)
+
+The options are marshalled to the output when running an app, under the
+`options` key. Here is an example of how the options are displayed (solve
+duration is displayed in `ns`):
+
+```json
+"options": {
+  "solve": {
+    "control": {
+      "bool": [],
+      "float": [],
+      "int": [],
+      "string": []
+    },
+    "duration": 10000000000,
+    "mip": {
+      "gap": {
+        "absolute": 0.000001,
+        "relative": 0.0001
+      }
+    },
+    "verbosity": "off"
+  }
+}
+```
+
+### Running locally
+
+CLI flags are added after the double-dash character (`--`):
+
+```bash
+go run . \
+  -runner.input.path input.json \
+  -runner.output.path output.json \
+  -solve.duration 10s
+```
+
+To set an environment variable, convert its corresponding CLI flag to uppercase,
+replacing each period (.) with an underscore (_) and removing the leading dash
+(-). For example: `-solve.duration` is equivalent to `SOLVE_DURATION`.
+
+```bash
+RUNNER_INPUT_PATH=input.json \
+RUNNER_OUTPUT_PATH=output.json \
+SOLVE_DURATION=10s \
+  go run .
+```
+
+(Note that there is no longer a need for the double-dash character.)
+
+If both an environment variable and its corresponding CLI flag are defined, the
+CLI flag will overwrite the environment variable.
+
+### Running remotely
+
+Use the `"options"` key in the `JSON` payload when executing a run on Nextmv
+cloud. The leading dash (`-`) is removed from the option name, when compared to
+running locally. For example, `-solve.duration` on a local run is equivalent to
+`solve.duration` when running remotely.
+
+:warning: Note that all values should be set as a `string`, regardless of the type.
+
+Here is an example of how to use options when running remotely:
+
+{% tabs %}
+{% tab label="JSON" language="json" %}
+
+```json
+{
+  "input": {},
+  "options": {
+    "solve.duration": "3s",
+    "solve.mip.gap.relative": "0.15",
+    "solve.verbosity": "high"
+  }
+}
+```
+
+{% /tab %}
+{% /tabs %}
+
+### Output
+
+Most options are parsed to the output, under the `options` key:
+
+```json
+"options": {
+  "solve": {
+    "control": {
+      "bool": [],
+      "float": [],
+      "int": [],
+      "string": []
+    },
+    "duration": 10000000000,
+    "mip": {
+      "gap": {
+        "absolute": 0.000001,
+        "relative": 0.0001
+      }
+    },
+    "verbosity": "off"
+  }
+},
+```
+
+You may also modify the options in your app code, which would override the ones
+passed from the runner.
+
+### Solver control parameters
+
+The Nextmv SDK has options for controlling the solver that work regardless of
+the provider being used. Some of these options include (using CLI-style flags):
+
+* `-solve.duration`: maximum duration of the solve.
+* `-solve.verbosity`: verbosity of the solver.
+* `-solve.mip.gap.relative`: relative gap for the MIP solver.
+* `-solve.mip.gap.absolute`: absolute gap for the MIP solver.
+
+Each provider has its own set of parameters for controlling their solver.
+Depending on the option’s data type, you can use one of the following flags to
+set these parameters (the list showcases CLI-style flags):
+
+* `-solve.control.bool`: parameters with `bool` values.
+* `-solve.control.float`: parameters with `float` values.
+* `-solve.control.int`: parameters with `int` values.
+* `-solve.control.string` parameters with `string` values.
+
+Each of these options receives a `name=value` pair. To set multiple options of
+the same type, use a comma-separated list: `name1=value1,name2=value2`. Note
+that not all providers support all data types.
+
+Here is an example where Nextmv SDK options are set alongside [HiGHS-specific
+options][highs-options] (using the Nextmv CLI). Notice that some options set
+multiple solver parameters.
+
+```bash
+nextmv sdk run . -- \
+  -runner.input.path input.json \
+  -runner.output.path output.json \
+  -solve.duration 10s \
+  -solve.mip.gap.absolute 80 \
+  -solve.mip.gap.relative 0.4 \
+  -solve.verbosity high \
+  -solve.control.float "mip_heuristic_effort=0.7" \
+  -solve.control.int "mip_max_nodes=200,threads=1" \
+  -solve.control.string "presolve=off"
+```
+
+Given that verbosity is set to `high`, the console will show the solver’s
+log (exposing that the options were set):
+
+```bash
+Running HiGHS 1.3.1 [date: 2023-01-01, git hash: abcd1234]
+Copyright (c) 2022 ERGO-Code under MIT licence terms
+Running with 1 thread(s)
+
+Presolve is switched off
+Objective function is integral with scale 1
+
+Solving MIP model with:
+   1 rows
+   11 cols (11 binary, 0 integer, 0 implied int., 0 continuous)
+   11 nonzeros
+
+        Nodes      |    B&B Tree     |            Objective Bounds              |  Dynamic Constraints |       Work      
+     Proc. InQueue |  Leaves   Expl. | BestBound       BestSol              Gap |   Cuts   InLp Confl. | LpIters     Time
+
+         0       0         0   0.00%   543             -inf                 inf        0      0      0         0     0.0s
+ S       0       0         0   0.00%   543             444               22.30%        0      0      0         0     0.0s
+
+Solving report
+  Status            Optimal
+  Primal bound      444
+  Dual bound        451
+  Gap               1.58% (tolerance: 40%)
+  Solution status   feasible
+                    444 (objective)
+                    0 (bound viol.)
+                    0 (int. viol.)
+                    0 (row viol.)
+  Timing            0.00 (total)
+                    0.00 (presolve)
+                    0.00 (postsolve)
+  Nodes             1
+  LP iterations     1 (total)
+                    0 (strong br.)
+                    0 (separation)
+                    0 (heuristics)
+```
+
+The output also shows the options that were used:
+
+```json
+"options": {
+  "solve": {
+    "control": {
+      "bool": [],
+      "float": [
+        {
+          "name": "mip_heuristic_effort",
+          "value": 0.7
+        }
+      ],
+      "int": [
+        {
+          "name": "mip_max_nodes",
+          "value": 200
+        },
+        {
+          "name": "threads",
+          "value": 1
+        }
+      ],
+      "string": [
+        {
+          "name": "presolve",
+          "value": "off"
+        }
+      ]
+    },
+    "duration": 10000000000,
+    "mip": {
+      "gap": {
+        "absolute": 80,
+        "relative": 0.4
+      }
+    },
+    "verbosity": "off"
+  }
+},
+```
+
+[nextmv-docs-integrations]: https://www.nextmv.io/docs/integrations/overview
+[ortools-section]: /mixed-integer-programming/supported-solvers#or-tools
+[highs-section]: /mixed-integer-programming/supported-solvers#highs
+[fico-xpress-section]: /mixed-integer-programming/supported-solvers#fico-xpress
+[pyomo-section]: /mixed-integer-programming/supported-solvers#pyomo
+[nextmv-docs-apps]: https://www.nextmv.io/docs/platform/topic-guides/apps
+[highs-options]: https://ergo-code.github.io/HiGHS/dev/options/definitions/
+[go-parse-duration]: https://pkg.go.dev/time#ParseDuration