Traces¶
Trace¶

class
mhi.enerplot.
Trace
(initializer=None, domain=None)¶ A trace is an array of numbers which hold the value of a signal as it changes over some domain. For instance, a trace may contain a voltage value as it changes over time.
Channels
andCurves
both extend from theTrace
class.
increasing
()¶ Test if a trace contains strictly increasing values.
A strictly increase trace is suitable to use as the domain of a dataset.
Returns: True
if every value is larger than the previous one.Return type: bool

decreasing
()¶ Test if a trace contains strictly decreasing values.
Returns: True
if every value is smaller than the previous one.Return type: bool

Basic Operations¶
Many basic operations are already possible on a Trace
.
All operations return a new trace; the original trace is unmodified.
Given a trace a
the following unary operations exist:
Operators  Operation 

len(a) 
Number of data points in the trace 
a[n] 
Access the nth data point in the trace 
a 
Negation 
abs(a) 
Absolute value 
math.ceil(a) 
Values rounded up to an integer 
math.floor(a) 
Values rounded down to an integer 
math.trunc(a) 
Values truncate towards zero 
Given two traces, a
and b
, or a trace and a scalar number
in either order, the following operations exist:
Operators  Operation 

a + b 
Addition 
a  b 
Subtraction 
a * b 
Multiplication 
a / b 
Division 
a ** b 
Exponentiation 
Note
If an operation is performed on two traces of different lengths, these operations will the result in a trace which matches the length of the shorter of the two traces. The extra data in the longer trace is ignored.
Convolution¶
Given two traces, a
and b
, the operation a @ b
returns
a convolution of the two traces.
For example, the given the Finite Impulse Response of a transfer function, the output signal can be created by convolving the input with the finite impulse response:
fir = mhi.enerplot.Trace([0.75, 1.0, 0.5, 0.25, 0.125])
output = input @ fir
The length of the output is 1 sample less than the sum of the lengths of the two input traces.
Other Operations¶
Additional operations on traces require importing methods from the
mhi.enerplot.math
library.
Example:
The following computed trace would approximate the full wave rectifier output:
from mhi.enerplot.math import minimum, maximum cigre = enerplot.datafile('Cigre_47.csv') a = cigre[r'Rectifier\AC Voltage:1'] b = cigre[r'Rectifier\AC Voltage:2'] c = cigre[r'Rectifier\AC Voltage:3'] rectifier_out = maximum(a, b, c)  minimum(a, b, c)
Logarthimic¶

mhi.enerplot.math.
exp
(trace)¶ Return a new trace where every value is transformed as: x → e^x.

mhi.enerplot.math.
ln
(trace)¶ Return a new trace where every value is transformed as: x → logₑ(x).
All values less than or equal to zero are replaced with
NaN

mhi.enerplot.math.
log
(trace, base=2.718281828459045)¶ Return a new trace where every value is transformed as: x → logₐ(x). The default base is “e”, for the natural logarithm.
All values less than or equal to zero are transformed to
NaN

mhi.enerplot.math.
log10
(trace)¶ Return a new trace where every value is transformed as: x → log₁₀(x).
All values less than or equal to zero are transformed to
NaN

mhi.enerplot.math.
sqrt
(trace)¶ Return a new trace where every value is transformed as: x → √x.
All values less than or equal to zero are transformed to
NaN
Circular¶

mhi.enerplot.math.
degrees
(trace)¶ Return a new trace where every value is transformed from radians to degrees.

mhi.enerplot.math.
radians
(trace)¶ Return a new trace where every value is transformed from degrees to radians.

mhi.enerplot.math.
sin
(trace)¶ Return a new trace where every value is transformed as: x → sin(x).
The input to the sin(x) function is intrepeted as being in radians.

mhi.enerplot.math.
cos
(trace)¶ Return a new trace where every value is transformed as: x → cos(x).
The input to the sin(x) function is intrepeted as being in radians.

mhi.enerplot.math.
tan
(trace)¶ Return a new trace where every value is transformed as: x → tan(x).
The input to the sin(x) function is intrepeted as being in radians.

mhi.enerplot.math.
asin
(trace)¶ Return a new trace where every value is transformed as: x → sin⁻¹(x).
The output of the sin⁻¹(x) function is in radians.
NaN
is returned for all values greater than 1, or less than 1.

mhi.enerplot.math.
acos
(trace)¶ Return a new trace where every value is transformed as: x → cos⁻¹(x).
The output of the cos⁻¹(x) function is in radians.
NaN
is returned for all values greater than 1, or less than 1.

mhi.enerplot.math.
atan
(trace)¶ Return a new trace where every value is transformed as: x → tan⁻¹(x).
The output of the tan⁻¹(x) function is in radians.

mhi.enerplot.math.
hypot
(x, y)¶ Compute a new trace, returning the Euclidean distance, sqrt(x*x + y*y), for each pair of values from the two input traces.
The follow two statements produce equivalent output:
from mhi.enerplot.math import hypot, sqrt c = hypot(a, b) c = sqrt(a ** 2 + b ** 2)
The first statement is significantly faster since the second statement requires allocating several temporary traces for holding the intermediate results.

mhi.enerplot.math.
atan2
(y, x)¶ Compute a new trace, returning the arc tangent (measured in radians) of y/x, for each pair of values from the two input traces. Unlike atan(y/x), the signs of both x and y are considered.
When used in conjunction with the
hypot()
, two traces representing real and imaginary values may be converted into two traces representing polar coordinates: magnitude and angle.
Selection¶

mhi.enerplot.math.
maximum
(*traces)¶ Return a new trace where the maximum value from each trace, at each point, is selected.

mhi.enerplot.math.
minimum
(*traces)¶ Return a new trace where the minimum value from each trace, at each point, is selected.
Processing¶

mhi.enerplot.math.
smooth
(trace, time_constant, domain)¶ Return a smoothed version of the input trace.
This function simulates a lag or ‘real pole’ function. The time domain solution algorithm is based on the trapezoidal rule. The solution method for this function is as follows:
Parameters:  trace (Trace) – the input to be smoothed.
 time_constant (float) – the timeconstant to be used for smoothing
 domain (float or trace) – the timestep, or the signal domain
Examples
If
input
represents aCurve
from aDataFile
with a 50µs timestep, the following statements would produce the same output:from mhi.enerplot.math import smooth output = smooth(input, 0.001, 50e6) output = smooth(input, 0.001, input.domain)