The Nematrian website: Expression
Evaluation
[this page  pdf  back links]
One of the tools available on the Nematrian website is its
Expression Evaluator. This tool allows users to use formulae rather than just
numbers as inputs to online computations.
As with interactive use of individual Nematrian function
webpages, the results are typically returned in the form of a hyperlink that
embeds the input parameters used to carry out the calculation, to make it
easier to check, reproduce or modify calculations at a later date. If results
are charts then the same hyperlink embedding is also typically used. For
example, if you wanted to move the legend in the following chart from above the
figure to below it you could do so by clicking on the chart, altering the
relevant ChartFormat parameter and then pressing the recalculate button
on the page you landed on when you clicked on the chart.
There are four main ways of using the Expression Evaluator:
(a) Insert an
expression into the text box on the expression evaluator
page and then press Calculate. This will then evaluate the expression
within the text box.
(b) Insert an expression
into the Search / Calculate textbox at the top of any page on the website and press
Calc button next to it. This replicates (a) but without needing to go to
expression
evaluator page beforehand.
(c) Enter an
expression into an input text box in the interactive input table on any page
summarising a specific Nematrian web function having checked the corresponding
box under the column headed “An expression input?” and then press the Calculate
button. The relevant input element of the Nematrian function is then taken as
the output of the relevant expression. The page relating to any particular
Nematrian function can be found from the list of Nematrian web
functions or by searching the Nematrian website).
(d) Use an expression as
an input to the (Mn)Evaluate
function (and set its Language input parameter to blank) as this effectively
replicates the output of the expression evaluator.
Formulae input into the expression evaluator
are interpreted using a relatively simple syntax in line with typical algebraic
conventions, i.e.:

Recognised algebraic operators are + (plus),  (minus), * (multiply), /
(divide) and ^ (power).

Recognised logical operators are TRUE and FALSE, “>” (greater than),
“<” (less than), “>=” (greater than or equal), “<=” (less than or
equal), “=” (equals), “And” (logical and), “Or” (logical or), “XOr” (logical
exclusive or, i.e. true if either x or y is true but not if both of them are
true) and “Not”

Order of evaluation is (i) Brackets (i.e. “(“ and “)”) and function
evaluation, see below), (ii) power, (iii) mutiply and divide, then (iv) add and
subtract

All Nematrian Web functions are recognised, either including their
leading “Mn” or without this prefix. Parameters follow immediately afterwards
in brackets, with consecutive input parameters (if any) separated by commas. If
an input parameter is an array then it should be enclosed in brackets with consecutive
elements separated by commas.

Any dates and times should be entered either using the format
#YYYYMMDD# or #YYYYMMDDTHH:MM:SS# or using Nematrian functions that return
values that are Dates, e.g. (Mn)DateSerial, (Mn)TimeSerial and (Mn)DateAndTimeSerial.

Integer values are automatically converted to Floating Point (i.e.
“Double” aka Double Precision) values if necessary.
Note
(1) Websites /
browsers can be cautious if you enter “<” and “>” into text boxes
(because it is possible to make malicious use of inputs that include these
characters). If you come across this problem with this website then you can work
around this issue by using the GT,
GTE, LT and LTE functions, which return
equivalent logical results to the >, >=, < and <= operators.
(2) It is not
currently possible to use the expression evaluator recursively within itself. Functions
such as (Mn)Evaluate, (Mn)EvaluateUsing, (Mn)EvaluateMultiValues,
(Mn)EvaluateExpressionsUsing
and (Mn)EvaluateExpressionsMultiValues
will not therefore be evaluated by the expression evaluator. Neither will
plotting functions that make use of the expression evaluator such as (Mn)PlotExpression, (Mn)PlotExpressions
and (Mn)PlotXYExpressionGeneral.
Other more specialist plotting functions such as (Mn)ProbDistPlotPdf
can be called via the expression evaluator, as illustrated below:
Important notice
If you use any Nematrian web service either programmatically
or interactively then you will be deemed to have agreed to the Nematrian
website License
Agreement.
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