The following Maths Functions come bundled with RiskScape for use in your function.
Built-in maths functions
RiskScape comes with a set of default functions that are useful for doing mathematics
in the context of RiskScape and Risk Analysis. They are used like any other RiskScape function.
For example, to round a floating point number, you can use the
round function like
Where possible, RiskScape makes use of maths packages that are part of the Java language.
These packages are widely used and are proven to produce reliable mathematical results.
For example, the
square_root() RiskScape function is just a simple ‘wrapper’ for the
More specific help for all these built-in functions is available from RiskScape’s built-in help.
From the command line, you can use
riskscape function list to see what functions are
available, the arguments each function takes, and what they return.
To list the maths functions available in RiskScape, run
riskscape function list --category maths.
Gives the absolute value of a number
Round number up to the closest integer
Returns Euler’s number (e) raised to the power of the value given. The inverse of log()
Convert input to a floating point number
Round number down to the closest integer
Convert input to a integer number
Return the logarithm of a number for a particular base, defaulting to natural log if none given
Returns the base-10 logarithm of the given value
Cumulative probability distribution function from a log-normal curve. Where shape is σ (standard deviation) and scale is μ (mean), both as the log of the distribution.
Probability Density Function (PDF) for a given point in a normal distribution. Where shape is σ (standard deviation) and scale is μ (mean), both as the log of the distribution.
Returns the greater of two values given
Returns the smaller of two values given
Cumulative probability distribution function from a normal curve
Probability Density Function (PDF) for a given point in a normal distribution
Computes a polynomial expression, denoted by the set of coefficients ‘c’ (starting at x⁰, x, x², etc)
Raise a number by a specific power
Picks an item from the list at random, or with an optional weighted probability
Returns a random number from the given normal distribution
Returns a random number within the range [start, stop]
Round number to the closest integer
Get the square root of the given number
Jython discrete functions
The following sections describe using RiskScape-based code from within a Jython function. Most Python users will probably find it simpler to setup RiskScape to use CPython and use standard Python maths packages instead.
A discrete function can be constructed from points, constants and other functions, to form a single function for use with risk analysis.
The simplest use of a discrete function is to join up a series of points to create a continuous sequence of lines between them.
from nz.org.riskscape.engine.function import DiscreteFunction ID = 'joined-points' DESCRIPTION = 'Demonstrates a function built by connecting points to form a series of linear functions' FUNCTION = DiscreteFunction.builder() \ .addPoint(-1, 4) \ .addPoint(1, 6) \ .addPoint(4, 8) \ .addPoint(10, 10) \ .withLinearInterpolation() \ .build()
As well as adding a point, a constant value can be added for a range:
# will return 0.45 when 0 <= x <= 10 DiscreteFunction.builder().addConstant(0, 10, 0.45)
Arbitrary RiskScape functions can be joined up to form a single function. Each function is added along with the range for which it’s applicable:
from nz.org.riskscape.engine.function import DiscreteFunction, Maths ID = 'joined-polynomials' DESCRIPTION = 'Demonstrates a function built by connecting polynomials' quadratic = Maths.newPolynomial(0, 8, 0.25) cubic = Maths.newPolynomial(10, 0, 4, 0.5) FUNCTION = DiscreteFunction.builder() \ .addFunction(-10, -5, cubic) \ .addFunction(40, 1000, polynomial) \ .withLinearInterpolation() \ .build()
By default, a discrete function will ‘close’ any upper bound on a range that
isn’t connected to a higher range. For example, adding the range
addFunction(0, 10, somePolynomial) will make that polynomial
0 <= x <= 10. However, if a function is added from 10 onwards,
somePolynomial applies when
0 <= x < 10.
This closing behaviour can be disabled by calling
on the function builder.