This is a basic question on the use of Trace Tables to assist in a dry run of a simple algorithm.
What I find most tricky is when to take a new line in the trace table? For example, take the following question:
Here is the array of integers which it applies to:
The following trace table is presented as one completes a dry run. Here is the solution:
I understand that initialising the variables Number, Lower & Upper appear on the first line, but when I go into the While Loop, I am tempted to put the value 5 on the first line also, for the variable Current. In essence, this is what I am tempted to do:
Why does this solution require that the value for Current, which is 5, appear on the second line? I suppose the question could be rephrased to 'When do I take a new line in a trace table?'
Thanks.
I think there is no specific way to do trace table, which means you have to setup your rules before you work and go on.
consider this example:
and this also:
did you notice the difference between loop iterator in each one. In first example they put the initialization value of the iterator in first line, and in second example they put the initialization of the loop iterator in the second line.
also have a look at wiki they also put the loop initialization in the second line.
also this video has similar example to those I posted here and is always start loop iterator in the second line.
also this example has totally different approach, which is each line of code in a new line in the trace table.
you can find also another different approach for trace table here
Finally:
In my opinion chose the rules that make sense for you, for example:
1-first line will contain the default values for the variables.
2-regarding loop iterations, put loop iterator in the same line as the variables that affected by this iteration, like the second example I posted above.
regarding your question I think it's more clear to put Current first value 5 in the second line, so you can track what each loop iteration affect your variables in a clear way.
Related
I have some problems with OCAML I wrote this:
let visibility_graph observation memory =
Graph.add_node memory.graph observation.position
Graph.add_node memory.graph observation.spaseship;
but it's not working. However this is working:
let visibility_graph observation memory =
Graph.add_node memory.graph observation.position
You don't give enough information to give a full answer. However the code you show is completely consistent with your error reports. The first example appears to consist of two expressions (function calls) with no separator between them. To execute two expressions sequentially, you need a semicolon (;) between them.
The semicolon at the end of the first example appears to be misplaced. Things might work (depending on what the rest of your code looks like) if you just move this semicolon to the end of the previous line.
The second example looks like a ligitimate function defintion. Of course it's difficult to tell without knowing the definitions of all the identifiers used.
In the problem that I want to solve a well defined matrix has no empty rows or columns.
For example the matrix [[],[]] is not valid.
When I call the function first_column, how do I prevent to execute it if the matrix that I send as an argument is not valid as defined before?
first_column([],[],[]).
first_column([[H|T]|Tail],[H|Col],[T|Rows]):- first_column(Tail,Col,Rows).
Technically, what you're asking can be done by testing for an end-condition of a list with one element, rather than an empty list, based on the specs you gave.
first_column([[H|T]],[H],[T]).
first_column([[H|T]|Tail],[H|Col],[T|Rows]):- first_column(Tail,Col,Rows).
However, beyond your specs, I suspect that you'll also need to "transfer" your final Col,Rows to end variables, something like:
first_column([[H|T]],C,R,[H|C],[T|R]).
first_column([[H|T]|Tail],[H|C],[T|R],Col,Rows):-
first_column(Tail,C,R,Col,Rows).
The modified predicate would be called with initial conditions, like
first_column(List,[],[],Col,Rows).
I have this parameter as an array. The array is big, 100 cells. It is a parameter that can be initiated in omnet.ini file. The cells with even numbers should get value A and odd numbers should get value B. How can I do this in an automated manner?
Is there a way besides having all odd and even indices initiated one by one manually?
Wildcards can be useful but I do not know how to use them to separate odd and even indices.
Thanks.
You can access the actual module index with the index operator. Combining this with the conditional operator ?: you can easily define the value:
**.myModule[*].myParameter = index % 2 == 0 ? "A" : "B"
I'm not aware of any feature like this. There are a number of work-arounds you could use:
Provide two parameters and select the correct one in code
Use the volatile keyword (probably not appropriate here)
Put the entire thing in your .ini file
I'd personally implement the first approach, that way you can use the wildcard to pass both parameters ([*].myNode.parameterEven and [*].myNode.parameterUneven) and then set the correct values in your array in a for loop.
However, you could also use the volatile keyword in your NED file, see the manual for more details. However, this approach mostly works well if you have different parameters depending on which node you are assigning it to. For this case I think the first approach is better.
The last alternative is just putting the entire thing in your .ini file, which may be useful if you want to parameterize the array later.
It has been a while since I've used Mathematica, and I looked all throughout the help menu. I think one problem I'm having is that I do not know what exactly to look up. I have a block of code, with things like appending lists and doing basic math, that I want to define as a single variable.
My goal is to loop through a sequence and when needed I wanted to call a block of code that I will be using several times throughout the loop. I am guessing I should just put it all in a loop anyway, but I would like to be able to define it all as one function.
It seems like this should be an easy and straightforward procedure. Am I missing something simple?
This is the basic format for a function definition in Mathematica.
myFunc[par1_,par2_]:=Module[{localVar1,localVar2},
statement1; statement2; returnStatement ]
Your question is not entirely clear, but I interpret that you want something like this:
facRand[] :=
({b, x} = Last#FactorInteger[RandomInteger[1*^12]]; Print[b])
Now every time facRand[] is called a new random integer is factored, global variables b and x are assigned, and the value of b is printed. This could also be done with Function:
Clear[facRand]
facRand =
({b, x} = Last#FactorInteger[RandomInteger[1*^12]]; Print[b]) &
This is also called with facRand[]. This form is standard, and allows addressing or passing the symbol facRand without triggering evaluation.
I have been working on a code in prolog for a while now and it is near compiling worthy and all my ideas seem to be solid so it should work when it compiles. It is a program that consults a database file for a list of clauses and then it awaits for a query by the user which it will then pick what information it needs from the sentence and query the database appropriately but there is a block of code that keeps giving me errors complaining that the flowpattern doesn't exist in the standard predicate this may be a silly question but even with all the looking into this I have done i can't find out how to fix this problem if someone could help me out or point me in the right direction that would be greatly appreciated.
Here is the block of code that gives the error:
loop(STR):-
scan(STR,LIST),
filter(LIST,LISroT1),
pars(LIST1,LIST2),
fail.
loop(STR):- STR >< "",readquery(L),loop(L).
readquery(QUERY):-nl,nl,write("Query: "),readln(QUERY).
scan(STR,[TOK|LIST]):-
fronttoken(STR,SYMB,STR1),!,
upper_lower(SYMB,TOK),
scan(STR1,LIST).
the specific line that the compiler complains about is fronttoken(STR,SYMB,STR),!,
any help will be apreaciated thanks!
Since we are looking at an "ex[c]er[p]t" of the code, it's hard to be sure what is going wrong, but the the given evidence points to this: loop/1 is being called before readquery/1 can do its work to populate (bind) the argument STR to loop/1.
Notice that loop/1 calls itself (recursively), and does so in a repeat/fail pattern. But the first time loop/1 runs, there's no indication in the code shown of how argument STR would get populated.
A clearer (more self-contained) code snippet would be like this:
loop :-
readquery(STR),
scan(STR,LIST),
filter(LIST,LISroT1),
pars(LIST1,LIST2),
fail.
loop :- loop.
This makes it clear that predicate loop doesn't actually return any result (and the given code snippet isn't complete enough to make clear what the program as a whole accomplishes). It assumes that the clauses ahead of fail in loop are deterministic, so that in failing, control passes through to the second (recursive) clause of loop/0. If this is not the case, the determinism could be forced by wrapping each call inside once/1.