Calc

Calc is a simple calculator that helps you to do simple math based on the latest measurement values.

Screenshot of the Calc module. Based on the current of the module SMU1, the variable 'Current density' is calculated in units of 'mA/cm^2' assuming an active area of 0.04 cm^2.

Usage

The typical way to use Calc involves the following steps:

1. Create a Calc module in the sequencer and change to the corresponding tab
2. Change the label of the module if desired
3. Enter a name of the calculated variable and its unit
4. Define whether the variable can be plotted and whether it should be saved
5. In section 'Values' create as many fields you need using 'Add value field'
6. Select the SweepMe! internal variables and relate them to 'x1', 'x2', and so on.
7. Type in your formula in section 'Formula' using 'x1', 'x2', etc. as placeholders for

Calc is performing its calculation when it is part of the active branch. It can process last known parameter values but has no access to the history of a parameter. The selected values can stem from modules that are present in the same branch, but also from modules in previously active branches.

Execution

Calc can calculate new values at different positions during the measurement procedure, e.g. before a new measurement point is set and measured or after all variables of a meaurement point have been taken.

• Always: Use this default value if you do not matter and just want to have actual values all the time. It is a combination of the other options.
• Before branch (in 'configure') calculates new values during the configure() phase of Calc and thus even before configure of child modules.
• Before each point (before 'start') calculates new values before the start() phase of all modules. The right order of modules in a branch are important. Arrange the modules in the order of how values must be processed.
• Before branch and each point (in 'configure' + before 'start') combines both of the above.
  In module versions before 2024-04-16 this option was called "At the beginning".
• After each point (in 'process') calculates new values when all Modules have measured their values during the process() phase.
  In module versions before 2024-04-16 this option was called "At the end".

Further information

• 'x0' is the last return value of the Calc module. It might be of interest to do some iterative recalculation and refinement. Please choose the correct execution, e.g. "At the beginning" or "At the end". Otherwise, the result will be modified twice per measurement point.
• 'x0' is always initialized as float('nan') (i.e. not a number of type float). You can test whether is x0 is such a 'nan' using isnan(x0)
• Several Calc modules can be used and combined to create more complex calculations.
• Calc only provides the data of the last measurement point, which can be 0-dimensional, e.g. in case of voltage, a time etc. or 1-dimensional, e.g. in case of a spectrum or a transient of an oscilloscope.
• If you need to access all points, that have been measured so far, the module CustomFunction is recommended that allows you to write your own python scrips and load additional libraries.

Examples

• Current density in mA/cm²: 1000 * x1 / x2 where x1 is the current of an SMU module in Ampere and x2 the active area of the sample in cm².
• Normalize spectrum by max: x1/max(x1) where x1 is a spectrum of a Spectrometer module.
• Calibrate temperatures: a * x1 + b where x1 is a measured temperature of the Temperature module and a,b are the coefficients of a linear calibration function.
• Sum up a value: x1 if isnan(x0) else x0 + x1 where x1 is the value to be summed up and x0 is the return value. Use Execution = "At the end". In the first step, y is set to x1, so that in subsequent steps x0 (which is the last y) is initialized to a start value.
• Create a message: "Ok" if x1 < 50 else "Warning" where x1 is a process parameter that is checked whether it would be ok 50 or not.
• Indexing: x1[62] where x1 is a variable with 1-dimensional data, e.g. a spectrum. Here, the value at index 62 is returned. Please note that indices start from 0.
• Peak position: min(x2[x1==max(x1)]) where x1 are 1-dimensional intensities and x2 are the corresponding 1-dimensional wavelengths. The function finds the first wavelength, the maximum value is achieved.
• String formatting: "%i" % x1 where x1 is an integer. Please note that the result will be a string.
• Create a message: "The measurement has finished" where no variable is needed. Such messages can be used to display them during a measurement in a Monitor widget.
• Print to debug (from version: 1.5.4.): print("My value is" , x1) where x1 can be any selected value. The output will be seen in the Debug window (F2).

Supported Functions

There is a limited number of functions that can be used inside the Calc module. The following list gives the commands that can be used in Calc and the corresponding python function that will be called. If there are further functions needed, please let us know (support@sweep-me.net).

The list is related to version: 1.5.4

python built-in functions

Calc command	Python function
abs	abs
len	len
max	max
min	min
int	int
float	float
round	round
str	str
repr	repr
print	print
type	type

datetime functions

Calc command	Python function
now	datetime.datetime.now

math functions

Calc command	Python function
ceil	math.ceil
degrees	math.degrees
fabs	math.fabs
floor	math.floor
fmod	math.fmod
frexp	math.frexp
hypot	math.hypot
ldexp	math.ldexp
modf	math.modf
pi	math.pi
pow	math.pow
radians	math.radians

random functions

Calc command	Python function
random	random.random
randint	random.randint

numpy functions

Calc command	Python function
sqrt	np.sqrt
absolute	np.absolute
real	np.real
imag	np.imag
angle	np.angle
conj	np.conj
sin	np.sin
sinh	np.sinh
asin	np.arcsin
arcsin	np.arcsin
cos	np.cos
cosh	np.cosh
acos	np.arccos
arccos	np.arccos
tan	np.tan
tanh	np.tanh
arctan	np.arctan
atan	np.arctan
arctan2	np.arctan2
atan2	np.arctan2
exp	np.exp
ln	np.log
log	np.log
log10	np.log10
average	np.average
mean	np.mean
arange	np.arange
linspace	np.linspace
logspace	np.logspace
divide	np.divide
sum	np.sum
trapz	np.trapz
sign	np.sign
isnan	np.isnan

Modifications of isnan: returns False if object is no float, returns bool instead of np.bool_