Expression syntax

Why need expressions? Expression evaluations used in various DM2000 features:

• Define axis and serie expressions for curve transformations without actual data changes;
• Perform arbitrary calculations on columns and lines in the data windows;
• Evaluate formula with different values of parameters in special Calculator tool;
• Manually transform curves with visual feedback using Transformation dialog box;
• Fit numeric data with selected expression and found "best fit" parameters values.

Any expression in DM2000 consists of function and parameter names, operator signs, parenthesis and spaces. While all valid operators and, in general, internal functions are allowed in almost any expression, available set of parameters depends on the feature that uses given expression. All names are case-insensitive.

Built-in function names, X denotes argument(s):

• Trigonometric functions: ARCTAN(X), COS(X), SIN(X), TAN(X) - standard functions, DEG(X) - converts radians to degrees, RAD(X) - converts degrees to radians, PI function w/o parameters just returns "pi" number.
  
  
• Standard mathematical functions: ABS(X), EXP(X), LN(X), LOG(X), SQR(X), SQRT(X) and RANDOM function that has no parameters and returns random number from 0 to 1.
  
  
• Boolean logic functions: AND(X1,X2,...), OR(X1,X2,...), XOR(X1,X2,...) (multiple arguments are allowed!), TRUE and FALSE constants. Note that TRUE is equal to 1.0, FALSE is 0.0 real numbers, and you may freely mix numeric and Boolean expressions, but numeric function arguments must be exactly 0.0 or 1.0.
  
  
• Miscellaneous functions: FRAC(X) - returns fractional part of the argument, INT(X) - integer part; MAX(X1,X2,...), MIN(X1,X2,...) - found maximal/minimal value, ROUND(X) - rounds value, SGN(X) - returns argument sign (+1/-1).
  
  
• Special functions used in DM2000: Time - no arguments, returns GetTickCount(); f_VDP(Ra,Rb) - returns Van-der-Paw formfactor; Ro_VDP(Ra,Rb[Ohm]; d[cm]) - returns resistivity for Van-der-Paw four-probe method; GCX(M,Fi,Gx,Gy), GCX(M,Fi,Gx,Gy) - returns real and imaginary part of impedance Z for G-compensation method; OSCX(ZoX,ZoY,ZsX,ZsY,ZX,ZY), OSCX(ZoX,ZoY,ZsX,ZsY,ZX,ZY) - the same but for Open/Short compensation; InvCX(Re,Im), InvCY(Re,Im) - invert complex value; Table(X,C) - returns value from column C in the position of the internal calibration table (see Options|Application dialog box and Options|Install table commands) calculated by X value from table key column.

Operators:

• Standard set of arithmetic operators is supported: "+", "-", "*", "/",  "^"(power)
  
  
• Boolean logic operators: "<", "<=", "<>", "=", ">=", ">" return True (1.0) or False (0.0).

Parameter identifiers:

• Axis and serie expressions: a..z - column values, cx, cy - synonyms for X and Y columns (this feature allows you to use the same expression for different files), num - number of line in serie (relative, 0 means start line), absnum - number of line in the associated worksheet (absolute).
  
  
• Calculator tool (defined in Options|Calculator dialog box): a..z - column values, cx, cy - synonyms for X and Y columns (for worksheet calculator tool X,Y columns are defined in worksheet header, for plot calculator tool these values are not column values but the coordinates of the clicked point).
  
  
• Process|Calculation operation: same as the above, cx/cy meaning depends on active viewer (plot or worksheet).
  
  
• Process|Copy Function wizard: same as the above, but cy parameter means Y(X) values from the source data range.
  
  
• Transformation dialog box (Custom tab): the same as for serie expressions, additionally p1 and p2 parameters are allowed.
  
  
• NLSF fitter: the only allowed parameter identifiers are cx (for fitting function argument) and fit parameters (p1..p26).

Example: suppose that you want to plot data in log scale. You should open axis or serie properties dialog box and set appropriate expression: log(cx) and/or log(cy). If you set serie expression(s) only selected serie will be transformed; in case of axis expression all series will be transformed.

Another example: in many cases the electrical conductivity of semiconductors obeys so-called "activation law": R~exp(E_a/kT). You can easily linearize R(T) dependence by plotting ln(R) vs. 1/T: just set X expression ln(cx) and Y expression 1/cy.

Notice: DM2000 application supports global history list for all features that uses expressions. This list may be remembered as a part of configuration information.