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Replace: y = (double)(lstChars.ToString()); //error
with: y = Convert.ToDouble(lstChars.ToString());
You are attempting to perform a cast that is not implicit. You need to use the ConvertTo function to handle this type of cast. Also, if the string does not represent a double or has characters in it that would not be used to represent a double the cast will fail.
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y = Convert.ToDouble(lstChars.ToString()); gives the following error:
Input string was not in a correct format. what can I do about this?
Thanks for your reply.
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This error tells me that the string that you are passing in to be converted contains something other than numbers and a decimal point. For example if you pass in "A32.41" the conversion to double will fail. If you pass in "36.42" the coversion will pass. Look to see what the actual string is when you call the convert function.
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I'm just curious about something.
Say there is a parliamentary consituency with X number of voters. Candidates A, B, C and D are standing for election. There is also the possibility that a voter may abstane or they may spoil their paper. Thus when the results are announced it is stated how many votes each candidate received, how many abstaned, and how many spoiled ballot papers there were.
If X (the total number of eligible voters) is known. How many permutations of results will allow candidate A to win? (using a first-past-the-post system. i.e. the candidate with more votes than any other candidate. Spoiled papers and abstentions are ignored for a win)
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Hi Colin,
that should be simple:
- abstaned/spoiled can be ignored completely, so you can remove them immediately
(rather than after doing the permutations)
- so there remain four candidates ABCD, of their permutations obviously one quarter
has A first, hence winning.
the one slight inaccuracy is the small chance that first and second place have equal
number of votes (and hence are undecided both in result and in permutation order),
but then a revote would be required, and it would again be 1 out of 4.
Going for president in Scotland ??
Regards,
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Sorry, that's not quite what I wanted. I wanted to know how many permutations in total there would be. Also, permutations including absentee and spoiled votes do count since they are valid scenarios.
For example with an electorate of 2 the permutations are:
A B C D Absentee Spoiled
2 0 0 0 0 0 A wins
1 0 0 0 1 0 A wins
1 0 0 0 0 1 A wins
In the above, there are 3 permutations where A can win
If that chart were continued for an electorate of 45,000 voters, how many permuations would A win. Is there a formula that can calculate this?
Luc Pattyn wrote: Going for president in Scotland ??
Not quite, there are elections coming up in a little over a month and one of the "election communications" I got said that only C or D can win this seat. A or B cannot win. I just wanted to write back and claim false avertising on the grounds that mathematically there were so many permutations of results where A could indeed win the election.
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I'm still not with you, you gave no clue as to any difference between A,B,C and D,
so they all have equal chances, and hence A/B/C/D will each win with 25% probability.
To put it differently, there are many permutations that make A win, but a similar
set of permutations makes B (or C or D) win.
Or still differently: with the given info, there is absolute symmetry.
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So, what you are saying here is that (without spoiled or absentee ballots) there are 25% of possible permutations that allow a candidate to win. From your other post you possibly hinted that the total number of permutations was number of options (X) to the power of the number of electorate (Y): X^Y
So, discounting absentee and spoiled papers (which I don't want to do because they are valid options and do affect the balance) the number of permuations where A wins is (4^45000)/4
If that is right, then this gives me a start.
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Right, with the exception of a tie, as I mentioned earlier (which gets more unlikely
as the number of voters increases).
Of course you realize 4^45000 is a big number.
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also I am not convinced you should concentrate on the table of permutations, because
different lines have different probabilities, so counting the lines does not help.
As an example, assume two voters E and F; they each can vote A/B/C/D/absent/spoiled
(6 possibilities each), so there are in fact 36 different combinations (that you
would group in 30 lines):
A B C D ab sp count
2 0 0 0 0 0 1 requires E and F to both vote A
1 0 0 0 1 0 2 requires E to vote A and F to be absent, OR vice versa
1 0 0 0 0 1 2 requires E to vote A and F to spoil, OR vice versa
0 2 0 0 0 0 1 requires E and F to both vote B
0 1 0 0 1 0 2 requires E to vote B and F to be absent, OR vice versa
0 1 0 0 0 1 2 requires E to vote B and F to spoil, OR vice versa
0 0 2 0 0 0 1 requires E and F to both vote C
0 0 1 0 1 0 2 requires E to vote C and F to be absent, OR vice versa
0 0 1 0 0 1 2 requires E to vote C and F to spoil, OR vice versa
0 0 0 2 0 0 1 requires E and F to both vote D
0 0 0 1 1 0 2 requires E to vote D and F to be absent, OR vice versa
0 0 0 1 0 1 2 requires E to vote D and F to spoil, OR vice versa
1 1 0 0 0 0 2 requires E to vote A and F to vote B, OR vice versa
1 0 1 0 0 0 2 requires E to vote A and F to vote C, OR vice versa
1 0 0 1 0 0 2 requires E to vote A and F to vote D, OR vice versa
0 1 1 0 0 0 2 requires E to vote B and F to vote C, OR vice versa
0 1 0 1 0 0 2 requires E to vote B and F to vote D, OR vice versa
0 0 1 1 0 0 2 requires E to vote C and F to vote D, OR vice versa
0 0 0 0 2 0 1 requires E and F to both be absent
0 0 0 0 1 1 2 requires E absent and F spoil, OR vice versa
0 0 0 0 0 2 1 requires E and F to both spoil
Hope this helps.
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Does this help at all?
"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15
"Judge not by the eye but by the heart." - Native American Proverb
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I write a function called improd in m-file(bb.m).
% in bb.m file
function [ p, pmax, pmin ,pn ] = improd ( f, g )
% help22
fd=double (f);
gd=double (g);
p=fd.*gd;
pmax=max(p( );
pmin=min(p( );
pn = mat2gray(p);
But when I call improd function,it appears the error about Undefined
function improd.
>> f=[1 2 ; 3 4];
>> g=[1 2 ; 2 1];
>> improd(f,g);
??? Undefined command/function 'improd'.
How do I let matlan know that I have declare a fuction in m-file and I
want to use the function?
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Did you save the file in your Matlab working directory?
If not you will need to add the location to your Matlab path.
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Your function name must be the same name as your file name. Rename your file to improd.m .
-Sean
----
Shag a Lizard
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I am writing an app that will download a 60MB file to update a DB on 20 remote users that all have 144K air cards. the internet connection that host the DB has a max upload speed of 250kbps and upload of 1MB.
I am trying to figure out at what KB will the upload speed kill the download speed.
I am also trying to figure out how to randomize the times they download the file in a controlled manner on the update flag is tripped.
Rob
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It doesn't seem like a hard problem to solve... but I'm unsure:
"the internet connection that host the DB has a max upload speed of 250kbps and upload of 1MB" is the connection that is serving the 20 remote users? And is the upload 250k or 1M?
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hi everyone
how can generate 100,000 unrepeated 16 digital serial numbers that dont be consecutive.
please give me your ideas
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I've got a couple ideas, and I'd really like to help, but in order to do that, you need to explain what you mean by "not being consecutive".
If that really is what you mean, the numbers (1e16, 1e16 + 2, 1e16 + 4,...) will fit your criterion (all unique, not consecutive), but I suspect you mean something else (random perhaps?).
So what are these numbers, why do they all need to be distinct, and why do they need to not be consecutive? Answer that question and I promise I'll get back to you.
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A simple approach would be to split your serial number into two sections. One section contains a sequential number the other is a random number. The first section will make your number unique while the second makes it non-consecutive.
If you want to have some kind of validation for the numbers add a third section containing a hash of the first two.
Hope this helps.
Tim
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Actually, if I understand your algorithm correctly, I don't think it's the best thing to do. (Please correct me if I'm wrong though)
Basically, your set of numbers will be much less random than they should be (they will end up being much more evenly spread over the range than they would be if they were "really" random).
If you try to generate a list of a bunch of random and non-equal 4 digit numbers, the way I understand your algorithm works, it would do something like the following (got the random umbers on the right hand side from python).
10 . 47 = 1047
11 . 67 = 1167
12 . 77 = 1277
13 . 23 = 1323
14 . 01 = 1411
And you're saying that because of the numbers on the left, from 10 to 14, guarantee the numbers will be unique (which is true), and the ones on the right "randomize" the numbers. The problem is that your numbers aren't very random at all (not uniformly distributed in the range 1000-9999). If you generate 40 numbers this way, none of them will be over 5000. For a really random set of 40 different numbers, the chance would be somewhere around (but not equal to, because the numbers are all different) about (1/2)^40, which is no chance at all.
If you switch your algorithm around, by putting the random half first, you get something MUCH better. In this case, you would get the numbers 4710, 6711, 7712, 2313, 1114. Your numbers will be much, much, much more random. In this guys case, you'd generate 11 digit random numbers, and use the last 5 for the sequence. They still won't be as great as they could theoretically be. If, for example, you did statistical tests of these numbers, you would find that exactly 10% of the numbers end in 1, 10% in 2, and so on. Obviously that wouldn't be true of a "really" random set.
Basically the best way to do it is just generate random numbers in that range. There is about a one in 50 million chance you'll have overlaps if your random number generator is good.
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Nathan A. wrote: ...
The problem is that your numbers aren't very random at all (not uniformly distributed in the range 1000-9999).
...
Of cause your are right - this is why I called my "algorithm" a simple approach.
Nathan A. wrote: ...
If you switch your algorithm around, by putting the random half first, you get something MUCH better.
...
When I suggested to use two (or three) "sections" I didn't meant to place them specifically in that sequence, just that the number can be compsed of two parts, each designed to fullfill one of the requirements.
Nathan A. wrote: ...
Basically the best way to do it is just generate random numbers in that range.
...
IMO the "best way" depends on your requirements. If the numbers must be uniformly distributed, a well known and tested pseudo random nuber generator will be the best solution. The "used" numbers can be stored and each newly generated number can be compared with this list to guarantee it is unique.
However, if you just want to generate some serial numbers for your application, which must be unique and should not be consecutive (for some reason), this approach seems to be overkill.
Regards,
Tim
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The OP simply requested unrepeated, not random. Truly random numbers must be allowed to repeat (otherwise you are choosing from a smaller and smaller pool). For serial numbers Nathan's approach sounds fine, how you combine (or mangle) the two/three components depends on the user's requirements.
Another approach is to take the numbers 1,2 .. 100,000 and encrypt or hash them, but this is not as simple as Nathan's approach. If you encrypt them it is possible to find the original serial number if this is important.
Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."
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Agreed. The original post asked for "unrepeated" and "nonconsecutive". By itself, this is really easy (10^6, 10^6 +2, 10^6 + 4, ...), and so I simply assumed he misasked his question.
Specifically I assumed that he wanted a random sample from that range without replacement. Like I told him, without getting a better requirements list, it wasn't going to be possible to answer his question properly.
Assuming he means "a random sample without replacement", I think my method (just generate the numbers) is best. The only problem here is that there aren't any guarantees they are unequal.
If you could "fudge" the randomness a bit, a previous poster came up with a good method (although in his method, you should put the random portion of the numbers first, then the sequential part, to maximize randomness). That method would generate 100K numbers that will be close to uniformly distributed.
You could also generate the numbers randomly and just keep the already generated ones sorted, so you can just check to see if they are in the list. This would produce the most accurate result, although also would take the most work (you'd have to do an extra insert and search into some data structure for each of your 100K iteration).
Finally, if you are comfortable with the theoretical foundations of random number generators, you might have some interesting possibilities there. As you might know, many of the most common RNGs are "Linear congruential RNGS". Each RNG of this type is defined by 3 numbers, a, b, and m. You start with an initial seed, n_0, and the number that comes out is (a*n_0 + b) mod m. That is your random number. By reapplying the formula with the JUST generated number will get you your second random number and so on. As far as this class of generators goes, there is an art and a science to picking "good" numbers" I think if you worked at it for an hour, you could figure out how to pick a, b, and m such that you could get a "uniform random without replacement" sample of 100K. I would guess this could be "the best" way, but it would require a little mathematical knowledge (nothing you can't get in a couple hours on wikipedia), and if you didn't know what you were doing, it would be pretty easy to mess it up. (I haven't looked at this in a while, but I think if you pick a prime as close to (10^17 - 10^16) as possible, and then get REALLY REALLY big a and b, you'd be ok.)
On the other hand, if unique and non-consecutive is REALLY what he wants, the following will do the trick:
std::vector<double> myVector;
myVector.reserve(100000);
int inserted = 0;
double baseNum = pow(10, 16);
while (inserted != 100000)
{
myVector.push_back(baseNum);
baseNum += 2;
}
will do exactly that.
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Guess we had different takes on the original question, but it does raise some interesting ideas, as long as we agree that they may have nothing to do with the original post.
I was looking at the serial number aspect, which I interpreted to be the type of alpha-numeric key type things you have to type in to install some software. Here the requirements MAY be:
1. hard to create valid serial numbers without the exact algorithm
2. easy to check if a serial number is valid
For 100,000 serial numbers, with 16 digits, if all numeric then only 10^5 of 10^16 are valid, so if the numbers appear 'random', the chance of creating one by guessing is 1 in 10^11. If the digits can be alphanumeric then the chance is lower.
Tim's approach of mangling bits from a sequence number, a random number and some hash value is a simple solution to this, likely to be adequate for many applications. However, if these numbers are to be tested for validity in the field, it is vulnerable as it places the algorithm needed to generate the serial numbers actually in the field software, so is susceptible to reverse engineering. As to whether this is a problem depends on waht you are trying to achieve.
You can make it safer using public key cryptography. For example, if you were to encrypt the blocks{serial_000001, serial_000002, serial_000003.. etc} using an RSA private key, then you could decrypt using the RSA public key in your software. Only valid serial numbers would decrypt to something of the correct form. It would be very difficult to generate valid numbers without the private key. This can only be part of a security system, but is a relatively simple way to make keys that are hard to fake.
You could generate random numbers using linear congruences, 'good' here usually refers to mathematical randomness; the uniform (or specifically shaped) distribution and lack of hidden correlation, characteristics essential for their use in monte-Carlo simulations. There is lots on the web on this, Numerical Recipes have a simple canned routine. For serial numbers though, Random numbers don't have a simple way of determining if a particular number is valid.
Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."
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First I wanna tell u that I am not well in English.
I wanna get some help from you.
Now I am making a mathematics project with VB.NET.
My idea is type a mathematics equation into a textbox.
Example: e^x + ln x , 3x^2 + 5x - 2 , sin x - cos^2 x , etc.
I don't wanna write the whole equation in coding time.
I'll write each part of mathematics functions i.e, sin(), cos(), exp(),ln(), etc.. in coding time.
I wanna get that when I type a equation into textbox and then click to commandbutton, corresponding function will automatically work and generate the correct answer.
I will very thanks you if you can help my problem.
phowarso
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