• x: the only letter representing the independent variable, so use sin(x) not sin(u).
• +, -, *, /: binary operators, addition, subtraction, multiplication and division.
• (): Use parentheses if necessary, use x/(x+1) not x/x+1, the latter is the same as 2.
• exp(x), log(x): exponetial and logrithm functions.
• sin(x), cos(x), tan(x), ctan(x) (not cot(x)): standard trignometry functions.
• e: scientific notation, like 2.0e-12
• abs(x): absolute value
• rand(x): random number
• pi, e: constants pi=3.1415926....., e=2.78.....
• x^p: power function, where p is a decimal number.
• sqrt(x): square root function
• sinh(x), cosh(x), tanh(x): hyperbolic functions
• asin(x), acos(x), atan(x): inverse trignometry functions
• asinh(x), acosh(x), atanh(x): inverse hyperbolic functions
• j0(x), j1(x), jn(n,x): zero order, first order and n-th order Bessel functions
• y0(x), y1(x), yn(n,x): zero order, first order and n-th order Bessel functions of second kind
• gamma(x): Gamma function

Also He define some constants other than pi and e:

  /**
   * Boltzman Constant. Units erg/deg(K)
   */
    public static final double BOLTZMAN     = 1.3807e-16;
  /**
   * Elementary Charge. Units statcoulomb
   */
    public static final double ECHARGE      = 4.8032e-10;
  /**
   * Electron Mass. Units g
   */
    public static final double EMASS        = 9.1095e-28;
  /**
   * Proton Mass. Units g
   */
    public static final double PMASS        = 1.6726e-24;
  /**
   * Gravitational Constant. Units dyne-cm^2/g^2
   */
    public static final double GRAV         = 6.6720e-08;
  /**
   * Planck constant. Units erg-sec
   */
    public static final double PLANCK       = 6.6262e-27;
  /**
   * Speed of Light in a Vacuum. Units cm/sec
   */
    public static final double LIGHTSPEED   = 2.9979e10;
  /**
   * Stefan-Boltzman Constant. Units erg/cm^2-sec-deg^4
   */
    public static final double STEFANBOLTZ  = 5.6703e-5;
  /**
   * Avogadro Number. Units  1/mol
   */
    public static final double AVOGADRO     = 6.0220e23;
  /**
   * Gas Constant. Units erg/deg-mol
   */
    public static final double GASCONSTANT  = 8.3144e07;
  /**
   * Gravitational Acceleration at the Earths surface. Units cm/sec^2
   */
    public static final double GRAVACC      = 980.67;

  /**
   * Solar Mass. Units g
   */
    public static final double SOLARMASS    = 1.99e33;
  /**
   * Solar Radius. Units cm
   */
    public static final double SOLARRADIUS  = 6.96e10;
  /**
   * Solar Luminosity. Units erg/sec
   */
    public static final double SOLARLUM     = 3.90e33;
  /**
   * Solar Flux. Units erg/cm^2-sec
   */
    public static final double SOLARFLUX    = 6.41e10;
  /**
   * Astronomical Unit (radius of the Earth's orbit). Units cm
   */
    public static final double AU           = 1.50e13;