Add environment variable customization for solver paths

docs/03-solver-configuration.md

@@ -32,6 +32,30 @@ m.solver = :glpk  # or
 m.solver = :scip
 ```
 
+## Solver Path Customization
+
+By default, RAMS assumes that solvers are available in your system's PATH with their standard names. However, you can customize the path or name for any solver using environment variables:
+
+- `RAMS_SOLVER_PATH_CBC` - Override path for CBC (defaults to `coin.cbc`)
+- `RAMS_SOLVER_PATH_CLP` - Override path for CLP (defaults to `clp`)  
+- `RAMS_SOLVER_PATH_CPLEX` - Override path for CPLEX (defaults to `cplex`)
+- `RAMS_SOLVER_PATH_GLPK` - Override path for GLPK (defaults to `glpsol`)
+- `RAMS_SOLVER_PATH_SCIP` - Override path for SCIP (defaults to `scip`)
+
+For example, if you have GLPK installed in a custom location:
+
+```bash
+export RAMS_SOLVER_PATH_GLPK=/opt/glpk/bin/glpsol
+```
+
+Or if you want to use a specific version of CBC:
+
+```bash
+export RAMS_SOLVER_PATH_CBC=/usr/local/bin/cbc-2.10
+```
+
+These environment variables are particularly useful when you have multiple versions of solvers installed or when solvers are installed in non-standard locations.
+
 ## Solver Arguments
 
 Additional solver arguments can be passed as though they are command line flags. The following adds both `--dfs` and `--bib` arguments to the GLPK invocation.

lib/rams/solvers/cbc.rb

@@ -5,7 +5,7 @@ module Solvers
     # Interface to COIN-OR Branch-and-Cut
     class CBC < Solver
       def solver_command(model_path, solution_path, args)
-        ['coin.cbc', model_path] + args + ['printingOptions', 'all', 'solve', 'solution', solution_path]
+        [solver_executable('coin.cbc', 'cbc'), model_path] + args + ['printingOptions', 'all', 'solve', 'solution', solution_path]
       end
 
       private

lib/rams/solvers/clp.rb

@@ -5,7 +5,7 @@ module Solvers
     # Interface to COIN-OR Linear Programming
     class CLP < Solver
       def solver_command(model_path, solution_path, args)
-        ['clp', model_path] + args + ['printingOptions', 'all', 'solve', 'solution', solution_path]
+        [solver_executable('clp', 'clp'), model_path] + args + ['printingOptions', 'all', 'solve', 'solution', solution_path]
       end
 
       private

lib/rams/solvers/cplex.rb

@@ -12,7 +12,7 @@ def solve_and_parse(model, model_path, solution_path)
       end
 
       def solver_command(model_path, solution_path, args)
-        ['cplex', '-c', "read #{model_path}"] + args + ['optimize', "write #{solution_path}"]
+        [solver_executable('cplex', 'cplex'), '-c', "read #{model_path}"] + args + ['optimize', "write #{solution_path}"]
       end
 
       private

lib/rams/solvers/glpk.rb

@@ -5,7 +5,7 @@ module Solvers
     # Interface to the GNU Linear Programming Kit
     class GLPK < Solver
       def solver_command(model_path, solution_path, args)
-        ['glpsol', '--lp', model_path, '--output', solution_path] + args
+        [solver_executable('glpsol', 'glpk'), '--lp', model_path, '--output', solution_path] + args
       end
 
       private

lib/rams/solvers/scip.rb

@@ -11,7 +11,7 @@ def solve_and_parse(model, model_path, solution_path)
       end
 
       def solver_command(model_path, _solution_path, args)
-        ['scip', '-c', "read #{model_path}"] + args +
+        [solver_executable('scip', 'scip'), '-c', "read #{model_path}"] + args +
           ['-c', 'optimize', '-c', 'display solution', '-c', 'display dualsolution', '-c', 'quit']
       end
 

lib/rams/solvers/solver.rb

@@ -60,6 +60,11 @@ def solver_command(_model_file, _solution_path, _args)
         raise NotImplementedError
       end
 
+      # Get solver executable name, checking environment variable first
+      def solver_executable(default_name, solver_name)
+        ENV["RAMS_SOLVER_PATH_#{solver_name.upcase}"] || default_name
+      end
+
       def parse_solution(model, solution_text)
         lines = solution_text.split "\n"
         RAMS::Solution.new(

tests/test_solver_paths.rb

@@ -0,0 +1,91 @@
+require './lib/rams.rb'
+require 'test/unit'
+
+# Test for solver path environment variable customization
+class TestSolverPaths < Test::Unit::TestCase
+  def setup
+    # Clear any existing environment variables
+    @old_env_vars = {}
+    %w[CBC CLP SCIP CPLEX GLPK].each do |solver|
+      env_var = "RAMS_SOLVER_PATH_#{solver}"
+      @old_env_vars[env_var] = ENV[env_var]
+      ENV.delete(env_var)
+    end
+  end
+
+  def teardown
+    # Restore original environment variables
+    @old_env_vars.each do |key, value|
+      if value
+        ENV[key] = value
+      else
+        ENV.delete(key)
+      end
+    end
+  end
+
+  def test_cbc_default_solver_command
+    solver = RAMS::Solvers::CBC.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal 'coin.cbc', command[0]
+  end
+
+  def test_cbc_custom_solver_command
+    ENV['RAMS_SOLVER_PATH_CBC'] = '/custom/path/to/cbc'
+    solver = RAMS::Solvers::CBC.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal '/custom/path/to/cbc', command[0]
+  end
+
+  def test_clp_default_solver_command
+    solver = RAMS::Solvers::CLP.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal 'clp', command[0]
+  end
+
+  def test_clp_custom_solver_command
+    ENV['RAMS_SOLVER_PATH_CLP'] = '/custom/path/to/clp'
+    solver = RAMS::Solvers::CLP.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal '/custom/path/to/clp', command[0]
+  end
+
+  def test_scip_default_solver_command
+    solver = RAMS::Solvers::SCIP.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal 'scip', command[0]
+  end
+
+  def test_scip_custom_solver_command
+    ENV['RAMS_SOLVER_PATH_SCIP'] = '/custom/path/to/scip'
+    solver = RAMS::Solvers::SCIP.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal '/custom/path/to/scip', command[0]
+  end
+
+  def test_cplex_default_solver_command
+    solver = RAMS::Solvers::CPLEX.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal 'cplex', command[0]
+  end
+
+  def test_cplex_custom_solver_command
+    ENV['RAMS_SOLVER_PATH_CPLEX'] = '/custom/path/to/cplex'
+    solver = RAMS::Solvers::CPLEX.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal '/custom/path/to/cplex', command[0]
+  end
+
+  def test_glpk_default_solver_command
+    solver = RAMS::Solvers::GLPK.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal 'glpsol', command[0]
+  end
+
+  def test_glpk_custom_solver_command
+    ENV['RAMS_SOLVER_PATH_GLPK'] = '/custom/path/to/glpsol'
+    solver = RAMS::Solvers::GLPK.new
+    command = solver.solver_command('/path/to/model.lp', '/path/to/solution.sol', [])
+    assert_equal '/custom/path/to/glpsol', command[0]
+  end
+end