Expression Builder |
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Expression Builder |
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The Expression Builder allows you to build and evaluate complex expressions on a variety of objects in Flex. The expressions can include basic arithmetic operations, mathematical functions, and distributed values from surfaces and horizons.
Expressions can be evaluated for the following objects in Visual MODFLOW Flex:
•Data Explorer Object Operations:
oPoint, Polyline, and Polygon Elevations
oSurface Elevations
oMap Elevations
oEdit Properties
•Model Explorer Objects
oModel Properties (Edit Properties Dialog)
oBoundary Conditions (Edit Boundary Conditions Dialog)
oSurface Water (Edit Surface Water Network Dialog)
For Data Explorer Objects, the Expression Builder can be accessed by right-clicking on the object, selecting Settings... and clicking on the Operations node. Model Explorer objects, you can enter expressions directly in the Calculation toolbar (similar to what is shown in red below) or you can build expressions with the assistance of the Expression Builder (
button):
The Expression Builder can be used to construct mathematical expressions to specify variable property values (e.g. Kx, initial heads, Kd), boundary condition values (e.g. river conductance, constant head, etc.), or attribute values for shapes (e.g. points features in the Data Explorer). The Expression Builder is shown below for editing conductivity values. The Expression builder consists of five components:
1.Expression workspace: a workspace to build expressions;
2.Operators: basic arithmetic operators (e.g. addition, subtraction, multiplication, division, parentheses, and exponents);
3.Variables & Constants: a list of variables associated with the current model cell and constants
4.Data Objects: a list of supported data objects from the data explorer and model explorer windows
5.Functions: a list of supported mathematical, logical, and vector functions
Please Note: The expression builder is case sensitive.
The following operators are always available in the Expression Builder:
Operator |
Button |
Example |
Result |
|---|---|---|---|
Add |
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1+2 |
3 |
Subtract |
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4-3 |
1 |
Multiply |
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2*5 |
10 |
Divide |
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2/4 |
0.5 |
Open bracket |
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3*(5+2) |
21 |
Close bracket |
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Less Than |
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5<2 |
False |
Greater Than |
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5>2 |
True |
Equals |
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5=5 |
True |
Power |
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5^3 |
125 |
Please Note: The expression builder does not support spaces between operators
The expression builder includes a list of applicable model properties or boundary condition values as well as standard constants as described below.
The following grid-based variables are always available in the Expression Builder:
Variable |
Description |
|---|---|
$BOT |
cell bottom elevation |
$DX1 |
cell width in the x-direction |
$DY1 |
cell length in the y-direction |
$DZ |
cell thickness |
$MBOT |
model bottom elevation |
$X |
x-coordinate of grid cell centroid |
$Y |
y-coordinate of grid cell centroid |
Notes: 1 - finite difference grids only |
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The following variables are available in the Expression Builder during Model Property editing sessions:
Variable |
Description |
|---|---|
$OLD{fieldname} |
initial value of the specified field {fieldname} at the start of the edit session |
The following variables are available in the Expression Builder when assigning Boundary Conditions using polylines or polygons or using a (polyline or polygon) data object:
Variable |
Description |
|---|---|
$FACEAREA_NORTH |
area of the current cell projected onto the model-coordinate XZ plane |
$FACEAREA_TOP |
area of the current cell projected onto the XY plane (i.e. plan area) |
$FACEAREA_WEST |
area of the current cell projected onto the model-coordinate YZ plane |
$RCHLNG1 |
length of the intersection between the current cell and the input polyline |
$LENGTH1 |
percentage along the length of the polyline from the beginning of the polyline to the exit point of the polyline from the current cell |
$SEGMENT1 |
ID of the polyline intersecting the cell |
$UCTOCOND |
unit conversion factor for converting the length and time units used for hydraulic conductivity to the length and time units used for conductance |
Notes: 1 - polyline features only |
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The following variables are available in the Expression Builder during Boundary Condition editing sessions:
Variable |
Description |
|---|---|
$KX |
horizontal conductivity along X-axis |
$KY |
horizontal conductivity along Y-axis |
$KZ |
vertical conductivity |
$MBOT |
model bottom elevation |
$OLD{fieldname} |
initial value of the specified field {fieldname} at the start of the edit session |
The following constants are always available in the Expression Builder:
Keyword |
Constant |
Example |
Result |
|---|---|---|---|
false |
False (constant) |
false |
0 |
pi |
Pi (π) (constant) |
pi cos(pi) |
3.14159265358979 -1 |
true |
True (constant) |
true |
1 |
The Data Objects component of the Expression Builder includes a list of objects from the Data Explorer and the Model Explorer windows that can be included in expressions. Surfaces and horizons are currently supported. Values from the surface/horizon are bilinearly interpolated to the location of the cell centroid (in the case of finite difference grid and quadtree grids) and to the interior cell node (in the case of Voronoi grids). Note that bilinear interpolation is exptrapolated beyond the extents of a given surface.
The syntax to use a surface is $`object_name` where object_name is the name of the surface in the Data Explorer or the name of the horizon in the Model Explorer, as applicable. Surfaces may be used in expressions:
•The expression $`Ground`($X $Y)-1 would result in a value of 1 unit of length below ground surface. This may be useful when defining features such as the bottom elevation of a river.
•The expression pmin($`Ground`($X $Y) $'Pit Elev'($X $Y)) would result in the lower elevation between ground surface and a surface representing the elevation of an excavated pit.
•The expression ifgaps($`local`($X $Y) $`regional`($X $Y)) compares local surface with a regional surface and uses the regional values where there are gaps in the local surface - this is useful with two surfaces have differing extents
The following functions are always available in the Expression Builder:
Function |
Description |
Example |
Result |
|---|---|---|---|
abs |
Absolute Value |
abs(-1.2) |
1.2 |
average |
Average |
average({1 2 3}) |
2 |
cif |
Conditional If |
cif(true 23 24) cif(false 23 24) cif(1 23 24) cif(0 23 24) cif(1-1 23 24) |
23 24 23 24 24 |
cos |
Cosine |
cos(0) |
1 |
dot |
Dot Product |
dot({1 2 3} {1 2 3}) |
14 |
equal |
Equality |
equal(2+2 4) equal(2+2 5) cif(equal(2+2 5) 23 24) |
1 0 24 |
exp |
Exponential |
exp(1) |
2.71828182845905 |
ifgaps |
Conditional If for noData values in a surface |
ifgaps(surfA surfB) |
returns surfA where it has valid values and surfB where it is absent or has noData values. surfA can be an expression |
ln |
Natural logarithm |
ln(2.718218) |
1 |
log |
Logarithm |
log(16 4) |
2 |
log10 |
Base-10 logarithm |
log10(100) |
2 |
max |
Maximum Value |
max({10 2.2 34}) |
34 |
min |
Minimum Value |
min({10 2.2 34}) |
2.2 |
mod |
Modulo |
(10)mod(3) |
1 |
mult |
Multiplication |
mult({2.0 3.0 4.0}) |
24 |
not |
Negation |
not(true) not(false) not(1) not(0) not(2) not(1-1) |
0 1 0 1 0 1 |
pmax |
Maximum Value (pairwise) |
pmax(1 2) |
2 |
pmin |
Minimum Value (pairwise) |
pmin(1 2) |
1 |
round |
Round to Decimal Place |
round(1.523 2) round(5.523 0) |
1.52 10 |
sigdig |
Round to significant digit |
sigdig(1523 2) sigdig(1.523E+3 1) |
1500 2000 |
sin |
Sine |
sin(pi/2) |
1 |
sqrt |
Square Root |
sqrt(4) |
2 |
sum |
Sum |
sum({1 2 3}) |
6 |
tan |
Tangent |
tan(pi/4) |
1 |
vector |
Vector |
vector({3 2}) |
{2.0 2.0 2.0} |
vequal |
Vector Equality |
vequal({1 2 3} {1 2 3})
cif(vequal({4 5 6} |
true
20 |
Examples are also provided in the help text, which you can view by hovering the mouse pointer over a given function.
Page url:http://www.waterloohydrogeologic.com/help/vmod-flex/index.html?vm_field-calculator.htm
