tcl error "expected floating point number but got" - tcl

Question

I am using tcl with the OpenSees program (see this question). One command offered by OpenSees in TCL is block2D and its syntax is as follows:
block2d $nx $ny $e1 $n1 element elementArgs {
1 $x1 $y1 <$z1>
2 $x2 $y2 <$z2>
3 $x3 $y3 <$z3>
4 $x4 $y4 <$z4>
}
In my specific case I am doing the following:
#geometric parameters
set nx 4
set ny 2
set elwidth 1.0
set elheight 1.0
set blockwidth [expr $nx*$elwidth]
set blockheight [expr $ny*$elheight]
block2D $nx $ny 1 1 quad "1 PlaneStrain2D 1" {
1 0.0 0.0
2 $blockwidth 0.0
3 4.0 2.0
4 0.0 2.0
}
Where the variables used in the block2D command are set in the beginning. Unfortunately when I run this script I get the following error:
WARNING block2D numX? numY? startNode? startEle? eleType? eleArgs?: invalid node coordinate for node: 1
expected floating-point number but got "$blockwidth"
I don't understand why this is happening. Other OpenSees commands allow for passing in variables. Why would this one be any different?
I have already tried different variants and nesting of the expr and eval commands on the blockwidth variable... All to no avail ...

Answer 1

The problem is that you've asked for an unsubstituted literal in this command:
block2D $nx $ny 1 1 quad "1 PlaneStrain2D 1" {
1 0.0 0.0
2 $blockwidth 0.0
3 4.0 2.0
4 0.0 2.0
}
That's what being in {braces} actually means. Which would be fine except you want a substitution in it. There are several sensible ways to do this:
Use a "double-quoted" word
block2D $nx $ny 1 1 quad "1 PlaneStrain2D 1" "
1 0.0 0.0
2 $blockwidth 0.0
3 4.0 2.0
4 0.0 2.0
"
Use the subst command
block2D $nx $ny 1 1 quad "1 PlaneStrain2D 1" [subst {
1 0.0 0.0
2 $blockwidth 0.0
3 4.0 2.0
4 0.0 2.0
}]
Use list to build the list
block2D $nx $ny 1 1 quad "1 PlaneStrain2D 1" [list \
1 0.0 0.0 \
2 $blockwidth 0.0 \
3 4.0 2.0 \
4 0.0 2.0 \
]
This third option is probably the best in terms of performance, but the second is probably more readable (despite being slowest), especially if you don't like using multi-line “strings” like the first option.