Clarify the code intent (#839)

Co-authored-by: Sean McLeod <sean@seanmcleod.com>

src/math/FGTable.cpp

@@ -491,6 +491,7 @@ double FGTable::GetValue(void) const
 
 double FGTable::GetValue(double key) const
 {
+ assert(nCols == 1);
  assert(Data.size() == 2*nRows+2);
  // If the key is off the end (or before the beginning) of the table, just
  // return the boundary-table value, do not extrapolate.
@@ -520,6 +521,7 @@ double FGTable::GetValue(double rowKey, double colKey) const
 {
  if (nCols == 1) return GetValue(rowKey);
 
+ assert(Type == tt2D);
  assert(Data.size() == (nCols+1)*(nRows+1));
 
  unsigned int c = 2;
@@ -550,6 +552,7 @@ double FGTable::GetValue(double rowKey, double colKey) const
 
 double FGTable::GetValue(double rowKey, double colKey, double tableKey) const
 {
+ assert(Type == tt3D);
  assert(Data.size() == nRows+1);
  // If the key is off the end (or before the beginning) of the table, just
  // return the boundary-table value, do not extrapolate.
@@ -575,6 +578,21 @@ double FGTable::GetValue(double rowKey, double colKey, double tableKey) const
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
+double FGTable::GetMinValue(void) const
+{
+ assert(Type == tt1D);
+ assert(Data.size() == 2*nRows+2);
+
+ double minValue = HUGE_VAL;
+
+ for(unsigned int i=1; i<=nRows; ++i)
+ minValue = std::min(minValue, Data[2*i+1]);
+
+ return minValue;
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
 void FGTable::operator<<(istream& in_stream)
 {
  double x;

src/math/FGTable.h

@@ -248,12 +248,31 @@ class JSBSIM_API FGTable : public FGParameter, public FGJSBBase
  /// The constructor for a table
  FGTable (std::shared_ptr<FGPropertyManager> propMan, Element* el,
  const std::string& prefix="");
- FGTable (int );
+ FGTable (int);
  FGTable (int, int);
+
+ /// Get the current table value
  double GetValue(void) const;
+ /// @brief Get a value from a 1D internal table
+ /// @param key Row coordinate at which the value must be interpolated
+ /// @return The interpolated value
  double GetValue(double key) const;
+ /// @brief Get a value from a 2D internal table
+ /// @param rowKey Row coordinate at which the value must be interpolated
+ /// @param colKey Column coordinate at which the value must be interpolated
+ /// @return The interpolated value
  double GetValue(double rowKey, double colKey) const;
+ /// @brief Get a value from a 3D internal table
+ /// @param rowKey Row coordinate at which the value must be interpolated
+ /// @param colKey Column coordinate at which the value must be interpolated
+ /// @param TableKey Table coordinate at which the value must be interpolated
+ /// @return The interpolated value
  double GetValue(double rowKey, double colKey, double TableKey) const;
+
+ double GetMinValue(void) const;
+ double GetMinValue(double colKey) const;
+ double GetMinValue(double colKey, double TableKey) const;
+
  /** Read the table in.
  Data in the config file should be in matrix format with the row
  independents as the first column and the column independents in

src/models/FGAtmosphere.cpp

@@ -125,14 +125,15 @@ double FGAtmosphere::ValidatePressure(double p, const string& msg, bool quiet) c
 
 double FGAtmosphere::ValidateTemperature(double t, const string& msg, bool quiet) const
 {
- // Using pressure in Outer Space between stars in the Milky Way.
- const double MinTemperature = ConvertToRankine(1.0, eKelvin);
- if (t < MinTemperature) {
+ // Minimum known temperature in the universe currently
+ constexpr double minUniverseTemperature = KelvinToRankine(1.0);
+
+ if (t < minUniverseTemperature) {
  if (!quiet) {
  cerr << msg << " " << t << " is too low." << endl
- << msg << " is capped to " << MinTemperature << endl;
+ << msg << " is capped to " << minUniverseTemperature << endl;
  }
- return MinTemperature;
+ return minUniverseTemperature;
  }
  return t;
 }

src/models/atmosphere/FGStandardAtmosphere.cpp

@@ -345,18 +345,26 @@ void FGStandardAtmosphere::SetTemperature(double t, double h, eTemperature unit)
 
 void FGStandardAtmosphere::SetTemperatureBias(eTemperature unit, double t)
 {
- unsigned int numRows = StdAtmosTemperatureTable.GetNumRows();
- const double minTemperature = StdAtmosTemperatureTable(numRows, 1) - 1.8;
+ // Retrieve the minimum temperature in the standard atmosphere, may not be the
+ // last row in future if for example it's extended and maybe there is some
+ // temperature inversion layer etc. So run through and find the minimum.
+ const double minStdAtmosphereTemp = StdAtmosTemperatureTable.GetMinValue();
+
+ // Minimum known temperature in the universe currently
+ constexpr double minUniverseTemperature = KelvinToRankine(1.0);
 
  if (unit == eCelsius || unit == eKelvin)
  t *= 1.80; // If temp delta "t" is given in metric, scale up to English
 
  TemperatureBias = t;
- if (TemperatureBias <= -minTemperature) {
+ // Confirm the temperature bias isn't going to result in an atmosphere
+ // temperature lower than the lowest known temperature in the universe
+ if (minStdAtmosphereTemp + TemperatureBias < minUniverseTemperature) {
+ double minBias = minUniverseTemperature - minStdAtmosphereTemp;
  cerr << "The temperature bias " << TemperatureBias << " R is too low. "
  << "It could result in temperatures below the absolute zero." << endl
- << "Temperature bias is therefore capped to " << -minTemperature << endl;
- TemperatureBias = -minTemperature;
+ << "Temperature bias is therefore capped to " << minBias << endl;
+ TemperatureBias = minBias;
  }
 
  CalculatePressureBreakpoints(SLpressure);
@@ -393,9 +401,11 @@ void FGStandardAtmosphere::SetSLTemperatureGradedDelta(eTemperature unit, double
 
 void FGStandardAtmosphere::SetTemperatureGradedDelta(double deltemp, double h, eTemperature unit)
 {
- unsigned int numRows = StdAtmosTemperatureTable.GetNumRows();
- const double minTemperature = StdAtmosTemperatureTable(numRows, 1);
- const double minDeltaTemperature = minTemperature - StdSLtemperature;
+ // Retrieve the minimum temperature in the standard atmosphere, may not be the
+ // last row in future if for example it's extended and maybe there is some
+ // temperature inversion layer etc. So run through and find the minimum.
+ const double minStdAtmosphereTemp = StdAtmosTemperatureTable.GetMinValue();
+ const double minDeltaTemperature = minStdAtmosphereTemp - StdSLtemperature;
 
  if (unit == eCelsius || unit == eKelvin)
  deltemp *= 1.80; // If temp delta "t" is given in metric, scale up to English

tests/unit_tests/FGTableTest.h

@@ -121,6 +121,46 @@ class FGTable1DTest : public CxxTest::TestSuite
  TS_ASSERT_EQUALS(t.GetValue(), 1.5);
  }
 
+ void testMinValue() {
+ FGTable t1(1);
+ t1 << 0.0 << 1.0;
+
+ TS_ASSERT_EQUALS(t1.GetMinValue(), 1.0);
+
+ FGTable t21(2);
+ t21 << 0.0 << -1.0
+ << 1.0 << 5.0;
+
+ TS_ASSERT_EQUALS(t21.GetMinValue(), -1.0);
+
+ FGTable t22(2);
+ t22 << 0.0 << 1.0
+ << 1.0 << -5.0;
+
+ TS_ASSERT_EQUALS(t22.GetMinValue(), -5.0);
+
+ FGTable t31(3);
+ t31 << 0.0 << -1.0
+ << 1.0 << 5.0
+ << 3.0 << 3.0;
+
+ TS_ASSERT_EQUALS(t31.GetMinValue(), -1.0);
+
+ FGTable t32(3);
+ t32 << 0.0 << 1.0
+ << 1.0 << -5.0
+ << 3.0 << 3.0;
+
+ TS_ASSERT_EQUALS(t32.GetMinValue(), -5.0);
+
+ FGTable t33(3);
+ t33 << 0.0 << 1.0
+ << 1.0 << 5.0
+ << 3.0 << -3.0;
+
+ TS_ASSERT_EQUALS(t33.GetMinValue(), -3.0);
+ }
+
  void testLoadInternalFromXML() {
  auto pm = make_shared<FGPropertyManager>();
  // FGTable expects <table> to be the child of another XML element, hence the