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define a simple model using an arithmetic expression

Syntax: mdefine<name>[<expression>[: [<type>] [<emin><emax>]]]

where <name> = the name of the model. If <name> is a previously defined model with mdefine, the current definition will overwrite the old one, and the user is warned. If it is a built-in model, the user will be asked to use a different name.

<expression> = a string of arithmetic expressions. Simple rules for expressions:

  1. The energy term must be 'e' or 'E' in the expression. Other words, which are not numerical constants nor internal functions, are assumed to be model parameters.
  2. If a convolution model varies with the location on the spectrum to be convolved, the special variable '.e' or '.E' may be used to refer to the convolution point.
  3. The expression may contain spaces for better readability.

<type> = user may optionally specify the type of the model. The valid types are add, mul, con. Mixing models are not yet implemented. Please note that the character ':' must be used to separate the options from the <expression>. If <type> is not given, the default is add.

<emin> <emax> = user may also specify the minimum and maximum energy values for the model. The default values are 1.e-20 and 1.e+20, respectively.

Note that mdefine can also be used to display and delete previously defined models:

  1. To display the name, type and expression of all previously defined models:
  2. To display the name, type and expression of a previously defined model by the name, MNAME:
    XSPEC12> mdefine MNAME
  3. To delete a previously defined model by the name, MNAME:
    XSPEC12> mdefine MNAME :


The following operators are recognized in an expression:

+ = plus operator
- = minus operator
$\ast$ = multiplying operator
/ = dividing operator
$\ast\ast$ = exponentiation operator
^ = exponentiation operator


The following internal functions are supported where expr is a vector (e.g. E):

unary functions
EXP (expr) = exponential
SIN (expr) = sine in radians
SIND (expr) = sine in degrees
COS (expr) = cosine in radians
COSD (expr) = cosine in degrees
TAN (expr) = tangent in radians
TAND (expr) = tangent in degree
SINH (expr) = hyperbolic sine in radians
SINHD (expr) = hyperbolic sine in degrees
COSH (expr) = hyperbolic cosine in radians
COSHD (expr) = hyperbolic cosine in degrees
TANH (expr) = hyperbolic tangent in radians
TANHD (expr) = hyperbolic tangent in degrees
LOG (expr) = base 10 log
LN (expr) = natural log
SQRT (expr) = square root
ABS (expr) = absolute value
INT (expr) = integer part
ASIN (expr) = inverse sine in radians
ACOS (expr) = inverse cosine in radians
ATAN (expr) = inverse tangent in radians
ASINH (expr) = inverse hyperbolic sine in radians
ACOSH (expr) = inverse hyperbolic cosine in radians
ATANH (expr) = inverse hyperbolic tangent in radians
ERF (expr) = error function
ERFC (expr) = complementary error function
GAMMA (expr) = gamma function
SIGN (expr) = -1 if negative, +1 if positive
HEAVISIDE (expr) = 0 if negative, +1 if positive
BOXCAR (expr) = +1 between 0 and 1, 0 otherwise
MEAN (expr) = mean value of the vector expression
DIM (expr) = dimension of the vector expression
SMIN (expr) = minimum value of the vector expression
SMAX (expr) = maximum value of the vector expression

binary functions
ATAN2 (expr1, expr2) = principal value of the arc tan of expr1/expr2 in radians
MAX (expr1, expr2) = maximum of the two expressions
MIN (expr1, expr2) = minimum of the two expressions

XSPEC Model Functions:

Any XSPEC model function (including models previously defined using mdefine) can be used in an mdefine expression. The complete name of the function must be used (no abbreviations) and the name should be followed by parentheses enclosing the function parameter values separated by commas. The energy is assumed and should not be included within the parentheses. For additive models the normalization parameter is not included within the parentheses but can obviously be added as a parameter in the expression.


//  define a model named "dplaw" with 3 parameters, p1, p2, f  
XSPEC12> mdef dplaw E**p1 + f*E**p2

// define a model named "junk" with 2 parameters (a, b)
XSPEC12> mdef junk a*e+b*log(e)/sin(e)  

// define a model named "junk2" with 1 parameter, a; the option 
//   following ":" says that it will be a multiplicative model. 
XSPEC12> mdef junk2  exp(-a*e) : mul   

// define a model named "junk3" with 1 parameter, B, options 
//   following ":" says that this will be a multiplicative model 
XSPEC12> mdef junk3  0.2+B*e : mul 

// try to define a blackbody model with name "bb", you get warning: 
XSPEC12> mdef bb E**2/T**4/(exp(E/T)-1) 

        ***Warning: bb is a pre-defined model
        Please use a different name for your model.

// this defines a Gaussian convolution model with sigma varying with 
//   square root of energy.
XSPEC12> mdef sg  exp(-E^2/(2*A*.E)) / sqrt(6.283*A*sqrt(.E))  :  con
// delete junk2 
XSPEC12> mdef junk2 :

// define a two-temperature model with common abundance and redshift
XSPEC12> mdef twotemp (1-f)*apec(T1,A,z) + f*apec(T2,A,z)

// define a pexrav model with parameter inclination instead of its cosine
XSPEC12> mdef mypex pexrav(g,f,refl,z,A,FeA,cos(Incl))

// define a model based on two other mdefine models
XSPEC12> mdef mymod junk3(p1)*junk(p2,p3)

// display all user-defined models
XSPEC12> mdef

Name ---- Type ---- Expression -----
dplaw     add       E**p1+f*E**p2
junk      add       a*E+b*LOG(E)/SIN(E)
junk3     mul       a+b*E
mymod     add       junk3(p1)*junk(p2,p3)
mypex     add       pexrav(g,f,refl,z,A,FeA,cos(Incl))
sg        con       EXP(-E^2/(2*A*.E))/SQRT(6.283*A*SQRT(.E))
twotemp   add       (1-f)*apec(T1,A,z)+f*apec(T2,A,z)

next up previous contents
Next: model (and rmodel) Up: Model Commands Previous: lumin