Expression syntax

Why need expressions? Language-independent expression evaluations used in various DM2003 features:

• Define axis and series expressions for curve transformations without actual data changes;
• Define worksheet columns expressions to display values of any function of worksheet data;
• Perform arbitrary calculations on columns and lines in the data windows;
• Evaluate formula with different values of parameters in special Calculator Dialog;
• Manually transform curves with visual feedback using Manual Fitter tool;
• Fit numeric data with selected expression and found "best fit" parameters values.

Any expression in DM2003 consists of function and parameter names, operator signs, parenthesis and spaces. While all valid operators and, in most cases, 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 DM2003: Time - no arguments, returns GetTickCount(); f_VDP(Ra,Rb) - returns van der Pauw formfactor; Ro_VDP(Ra,Rb[Ohm]; d[cm]) - returns resistivity for van der Pauw four-probe method; GCX(M,Fi,Gx,Gy), GCY(M,Fi,Gx,Gy) - returns real and imaginary part of impedance Z for G-compensation method; OSCX(ZoX,ZoY,ZsX,ZsY,ZX,ZY), OSCY(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:

• Plot axes, plot series and worksheet column 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 - relative number of line in the data series (0 means start line), absnum - absolute number of line in the associated worksheet (both used only for series expressions).
  
  
• Calculator Dialog (Process|Calculation|Calculator dialog): 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).
  
  
• Recalculate Data Range operation: same as the above, cx, cy meaning depends on active viewer (plot or worksheet).
  
  
• Copy Function Tool: same as the above, but cy parameter means Y(X) values from the source data range.
  
  
• Manual Fitter Tool: the same as for series expressions, additionally p1 and p2 parameters are allowed.
  
  
• NLSF Fitter Tool, LEVMAR Fitter Tool: the only allowed parameter identifiers are cx (for fitting function argument) and fitting parameters (p1..p26).
  
  
• General Linear Fitter Tool: basis terms must include only function argument (cx).
  
  
• Multi-X NLSF Fitter Tool: independent variables (function arguments) must be denoted cx1..cx26; fitting parameters are the same as in the standard NLSF Fitter Tool (p1..p26).

Notice: DM2003 application supports global history list for all features that uses expressions. This list may be remembered as a part of configuration information. Also, you can define your own functions for use in expression evaluator and in fitters.