I notice that there is a line that said
# Generated by using Rcpp::compileAttributes() -> do not edit by hand
in RcppExport.R.
But I wonder if there is the possibility that I could edit RcppExport.R by hand?
For example, I want to give a default value to one of my input a parameter.
Thank you!
You can set a default value the standard way, again following what both languages involved permit (i.e. if you set one, all following args need one too per C++ rules):
> Rcpp::cppFunction("double mySum(double a, double b=10) { return a+b; }")
> mySum(4)
[1] 14
> mySum(4,5)
[1] 9
>
More generally speaking, and as this is your third somewhat basic Rcpp question in the space of 24 hours, could I suggest the Introduction to Rcpp vignette, along with the other vignettes and maybe a look around the Rcpp Gallery ?
Related
I have a list of people and I want to pair them all then do some filtering based on preferences. When I generate my candidate solutions, how do I avoid creating candidate solutions that re-pair a people.
For example:
person(a;b;c;d) .
{match(X, Y): person(Y)}1 :- person(X) .
This generates candidate solutions that include match(a,b) match(c,b) ...
I would like ONLY candidate solutions that do not rematch anyone like: match(a,b) match(c,d) ...
My goal is to not have to filter rematches out via additional constraints. Also, not everyone needs to be matched. Thanks!
person(a;b;c;d).
{match(A,B) : person(A), person(B), A < B}.
:- person(A), 1 < {match(A,B); match(B,A)}.
You exclude solutions that have more than 1 match for a single person.
It is not possible to simply choose a correct set of atoms without additional constraints. As match(a,b) and match(b,c) can occur in different answer sets, both variables need to be created. Only a constraint can rule out that both do not occur in the same answer set.
Also note that your generator rule
{match(X, Y): person(Y)}1 :- person(X) .
already is a shortcut writing for
{match(X, Y): person(Y)} :- person(X).
:- person(X), 2 {match(X, Y): person(Y)}.
And therefore you are already using a constraint whenever your generator choice rule has non-trivial bounds.
PS: Check the different versions using --stats=2 for constraint count and --text for a rough approximation of what kind of constraints are generated.
I'd go for Max Ostrowskis answer.
One of the difficulties is to handle the order of the attributes for the match predicate: this is a tuple, there is a difference if your value shows up on first or second position. Adding a rule to make the predicate commutative should do the trick since you don't need to distinguish for a value to be on first or second position. This method does not use a constraint (on first sight), but it duplicates the generated values so the output differs from your desired solution. Also it adds a line to the code.
person(a;b;c;d).
{match(X,Y): person(Y), X!=Y}1 :- person(X).
match(Y,X) :- match(X,Y).
#show match/2.
Output
Answer: 1
Answer: 2
match(c,a) match(a,c)
Answer: 3
match(b,a) match(a,b)
Answer: 4
match(c,d) match(d,c)
Answer: 5
match(b,a) match(a,b) match(c,d) match(d,c)
Answer: 6
match(b,d) match(d,b)
Answer: 7
match(c,a) match(a,c) match(b,d) match(d,b)
Answer: 8
match(b,c) match(c,b)
Answer: 9
match(d,a) match(a,d)
Answer: 10
match(d,a) match(a,d) match(b,c) match(c,b)
SATISFIABLE
I have different commands my program is reading in (i.e., print, count, min, max, etc.). These words can also include a number at the end of them (i.e., print3, count1, min2, max6, etc.). I'm trying to figure out a way to extract the command and the number so that I can use both in my code.
I'm struggling to figure out a way to find the last element in the string in order to extract it, in Smalltalk.
You didn't told which incarnation of Smalltalk you use, so I will explain what I would do in Pharo, that is the one I'm familiar with.
As someone that is playing with Pharo a few months at most, I can tell you the sheer amount of classes and methods available can feel overpowering at first, but the environment actually makes easy to find things. For example, when you know the exact input and output you want, but doesn't know if a method already exists somewhere, or its name, the Finder actually allow you to search by giving a example. You can open it in the world menu, as shown bellow:
By default it seeks selectors (method names) matching your input terms:
But this default is not what we need right now, so you must change the option in the upper right box to "Examples", and type in the search field a example of the input, followed by the output you want, both separated by a ".". The input example I used was the string 'max6', followed by the desired result, the number 6. Pharo then gives me a list of methods that match that:
To get what would return us the text part, you can make a new search, changing the example output from number 6 to the string 'max':
Fortunately there is several built-in methods matching the description of your problem.
There are more elegant ways, I suppose, but you can make use of the fact that String>>#asNumber only parses the part it can recognize. So you can do
'print31' reversed asNumber asString reversed asNumber
to give you 31. That only works if there actually is a number at the end.
This is one of those cases where we can presume the input data has a specific form, ie, the only numbers appear at the end of the string, and you want all those numbers. In that case it's not too hard to do, really, just:
numText := 'Kalahari78' select: [ :each | each isDigit ].
num := numText asInteger. "78"
To get the rest of the string without the digits, you can just use this:
'Kalahari78' withoutTrailingDigits. "Kalahari"6
As some of the Pharo "OGs" pointed out, you can take a look at the String class (just type CMD-Return, type in String, hit Return) and you will find an amazing number of methods for all kinds of things. Usually you can get some ideas from those. But then there are times when you really just need an answer!
i am trying to print variables with indices.
The goal is to write something like:
x_1 + x_2 = 3 + 1 = 4
The problem is, that variables just like x_1 does not show an index. It shows the underscore itself.
/* works fine */
print(x_1)$
x_1;
/* Does not work */
ostream: make_string_output_stream()$
printf(ostream, string(x_1))$
get_output_stream_string(ostream);
Output of the code above
Converting "x_1" into a string destroys the underscore, but you need a string for the method printf().
Are there workarounds for this?
What to do here probably depends somewhat on what goal you need to achieve with this. Can you say more about the larger goal you are working toward?
In order to generate output which has typesetting instructions in it, you can call the tex or tex1 function to generate TeX output. If that needs to be displayed in a web page, I believe you can make use of the MathJax Javascript library. Sorry, I don't know more about MathJax.
You should probably write x[1] instead of x_1. Displaying x_1 with a subscript 1 is a convenience -- the rest of Maxima doesn't know much about it.
EDIT: There is also an add-on package to output MathML; there might be two such packages, I would have to check. If MathML could help solve your problem, I will look into it.
I've been looking all around the web for this answer and can't find it.
I'm semi new to python so hoping i get an answer here,
so basically what i want to do is, access a text file "number.txt"
that has a 10 as a line, and do a sum within the python code.
Here is what i got so far:
with open('number.txt', 'r') as sum:
num = sum.readline()
clean = num.rstrip('\n')
#number.txt file only contains 1 line and is a 10
increase = "5"
adding = clean + increase
print(adding)
it doesn't do the sum, instead i get the 5 added after the 10
so instead of getting 15 i get 105.
can anyone help?
Welcome to programming. Keep aware of the concepts of data types, I suggest doing some reading on that.
The + operator behaves differently between strings, arrays, and integers.
I would give you the answer but I am guess you are doing this as an assignment of sorts, so I just wanted to point you in the right direction. Use a python debugger (like PyCharm, or Wing IDE) to determine the differences between "5" + "10" 5+10 and [5]+[10]
You need to look into what's called Type Casting
I tried the following snippet of Alloy4, and found myself confused by the behavior of the util/Natural module. The comments explain more in detail what was unexpected. I was hoping someone could explain why this happens.
module weirdNatural
private open util/natural as nat
//Somehow, using number two obtained from incrementing one works as I expect, (ie, there is no
//number greater than it in {0,1,2}. but using number two obtained from the natrual/add function
//seems to work differently. why is that?
let twoViaAdd = nat/add[nat/One, nat/One]
let twoViaInc = nat/inc[nat/One]
pred biggerAdd {
some x: nat/Natural | nat/gt[x, twoViaAdd]
}
pred biggerInc {
some y: nat/Natural | nat/gt[y, twoViaInc]
}
//run biggerAdd for 10 but 3 Natural //does not work well, it does find a number gt2 in {0,1,2}
run biggerInc for 10 but 3 Natural //works as expected, it finds a number gt2 in {0,1,2,3}, but not in {0,1,2}
Thanks for this bug report. You are absolutely right, that is a weird behavior.
Alloy4.2 introduced some changes to how integers are handled; namely, the + and - operators in Alloy4.2 are always interpreted as set union/difference, so built-in functions plus/minus have to be used to express arithmetic addition/subtraction. On the other side, the util/natural module (mistakenly) hasn't been updated to use the latest syntax, which was the root cause of the weird behavior you experienced (specifically, the nat/add function uses the old + operator instead of plus, whereas nat/inc doesn't).
To work around this issue, you can either
open the util/natural module (choose "File -> Open Sample Models" from the main menu)
edit the file and replace the two occurrences of <a> + <b> with plus[<a>, <b>]
save the new file in the same folder with your model als file (e.g., as "my_nat.als")
open it from your main module (e.g., open my_nat as nat)
or
download the latest unofficial version where this bug is fixed (you might need to manually delete the Alloy temp folder to make sure that the Alloy Analyzer is not using the old (cached) version of the util/natural library).