I am used to programming PC's and smartphones using high level languages, microcontrollers are a new territory for me. Are they somehow different, more untrustworthy, requiring different techniques? Here is bit of code to write and read to EEPROM running on a Arduino Mega: (there is an Ethernet Shield attached, not used here)
#include <EEPROM.h>
int addr = 0;
int val;
byte value;
void setup()
{
Serial.begin(9600);
}
void loop()
{
val = 9;
EEPROM.write(addr, val);
delay(500);
addr = addr + 1;
if (addr == 20) addr = 0;
value = EEPROM.read(addr);
Serial.print(addr);
Serial.print("\t");
Serial.print(value);
Serial.println();
}
Heres what comes out:
1 91
2 91
3 9
4 9
5 9
6 9
7 9
8 9
9 9
10 9
11 9
12 202
13 202
14 202
15 202
16 202
17 202
18 202
19 202
0 9
1 89
2 91
3 9
4 9
5 9
6 9
7 9
8 9
9 9
10 9
11 9
12 9
13 9
14 9
15 9
16 9
.....
In general address 1 and 2 are always flaky and it takes two writes to change memory locations above ~10.
I can switch out another board and still get similar oddities.
How can I adapt my programming to this seemingly flaky performance?
Simply enough, your code is wrong.
Logically step through it. You are writing to an EEPROM at address addr. You then wait 500ms, increment addr, and then read from the new addr. The addr you read from is therefore not the addr you write to.
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The following code converts hour from 24hr format to 12hr format. The input is an integer Hrs_24_Format, which has possible values from 0 to 23.
if ( Hrs_24_Format > 12 )
Hrs_12_Format = Hrs_24_Format – 12;
else if (Hrs_24_Format == 0)
Hrs_12_Format = 12;
else
Hrs_12_Format = Hrs_24_Format;
How to develop this logic without any condition (no branching on its flowchart)?
Assuming Hrs_24_Format is an integer, this should do what you want:
(Hrs_24_Format + 11) % 12 + 1
This produces the following values:
0 12
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9
10 10
11 11
12 12
13 1
14 2
15 3
16 4
17 5
18 6
19 7
20 8
21 9
22 10
23 11
24 12
You can use a modulo calculation:
Hrs_12_Format = ((Hrs_24_Format + (12-1) % 12) + 1;
You need to temporarily subtract 1 from the input for the modulo operation in order to get values from 1 to 12 instead of from 0 to 11.
Then you also need to add a constant positive offset before subtracting 1, to avoid an underflow when the input is 0. Using any multiple of 12 mathematically has no effect on the result, so practically you just use 12.
Visualization:
0 1 2 ... 11 12 13 ... 22 23
+12-1: 11 12 13 ... 22 23 24 ... 33 34
% 12: 11 0 1 ... 10 11 0 ... 9 10
+1: 12 1 2 ... 11 12 1 ... 10 11
Note that the implementation of the modulo operator still has to use the condition "if x > 12" in some way under the covers. The branching is an inherent part of this calculation.
If you don't wish to use any conditional operators, and don't have any branches, a possible solution is:
#include<stdio.h>
#include <stdlib.h>
int main(int argc, char ** argv)
{
int Hrs_12_Format, Hrs_24_Format;
Hrs_24_Format = strtol(argv[1], NULL, 0);
Hrs_12_Format = (Hrs_24_Format +11)%12 +1)
printf("The 12 hour format is %d\n",Hrs_12_Format);
return 0;
}
Sample output:
./a.out 0
The 12 hour format is 12
./a.out 1
The 12 hour format is 1
./a.out 2
The 12 hour format is 2
./a.out 3
The 12 hour format is 3
.
.
.
./a.out 24
The 12 hour format is 12
./a.out 23
The 12 hour format is 11
I am trying to parse a VTK file in C by extracting its point data and storing each point in a 3D array. However, the file I am working with has 9 shorts per point and I am having difficulty understanding what each number means.
I believe I understand most of the header information (please correct me if I have misunderstood):
ASCII: Type of file (ASCII or Binary)
DATASET: Type of dataset
DIMENSIONS: dims of voxels (x,y,z)
SPACING: Volume of each voxel (w,h,d)
ORIGIN: Unsure
POINT DATA: Total number of points/voxels (dimx.dimy.dimz)
I have looked at the documentation and I am still not getting an understanding on how to interpret the data. Could someone please help me understand or point me to some helpful resources
# vtk DataFile Version 3.0
vtk output
ASCII
DATASET STRUCTURED_POINTS
DIMENSIONS 256 256 130
SPACING 1 1 1.3
ORIGIN 86.6449 -133.929 116.786
POINT_DATA 8519680
SCALARS scalars short
LOOKUP_TABLE default
0 0 0 0 0 0 0 0 0
0 0 7 2 4 5 3 3 4
4 5 5 1 7 7 1 1 2
1 6 4 3 3 1 0 4 2
2 3 2 4 2 2 0 2 6
...
thanks.
You are correct regarding the meaning of fields in the header.
ORIGIN corresponds to the coordinates of the 0-0-0 corner of the grid.
An example of a DATASET STRUCTURED_POINTS can be found in the documentation.
Starting from this, here is a small file with 6 shorts per point. Each line represents a point.
# vtk DataFile Version 2.0
Volume example
ASCII
DATASET STRUCTURED_POINTS
DIMENSIONS 3 4 2
ASPECT_RATIO 1 1 1
ORIGIN 0 0 0
POINT_DATA 24
SCALARS volume_scalars char 6
LOOKUP_TABLE default
0 1 2 3 4 5
1 1 2 3 4 5
2 1 2 3 4 5
0 2 2 3 4 5
1 2 2 3 4 5
2 2 2 3 4 5
0 3 2 8 9 10
1 3 2 8 9 10
2 3 2 8 9 10
0 4 2 8 9 10
1 4 2 8 9 10
2 4 2 8 9 10
0 1 3 18 19 20
1 1 3 18 19 20
2 1 3 18 19 20
0 2 3 18 19 20
1 2 3 18 19 20
2 2 3 18 19 20
0 3 3 24 25 26
1 3 3 24 25 26
2 3 3 24 25 26
0 4 3 24 25 26
1 4 3 24 25 26
2 4 3 24 25 26
The 3 first fields may be displayed to understand the data layout : x change faster than y, which change faster than z in file.
If you wish to store the data in an array a[2][4][3][6], just read while doing a loop :
for(k=0;k<2;k++){ //z loop
for(j=0;j<4;j++){ //y loop : y change faster than z
for(i=0;i<3;i++){ //x loop : x change faster than y
for(l=0;l<6;l++){
fscanf(file,"%d",&a[k][j][i][l]);
}
}
}
}
To read the header, fscanf() may be used as well :
int sizex,sizey,sizez;
char headerpart[100];
fscanf(file,"%s",headerpart);
if(strcmp(headerpart,"DIMENSIONS")==0){
fscanf(file,"%d%d%d",&sizex,&sizey,&sizez);
}
Note than fscanf() need the pointer to the data (&sizex, not sizex). A string being a pointer to an array of char terminated by \0, "%s",headerpart works fine. It can be replaced by "%s",&headerpart[0]. The function strcmp() compares two strings, and return 0 if strings are identical.
As your grid seems large, smaller files can be obtained using the BINARY kind instead of ASCII, but watch for endianess as specified here.
I'm tasked with implementing an algorithm which was supplied as Matlab (which none of us have any experience with) into our c++ application.
There is an array declared as such:
encrypted = [18 10 20 13 6 25 21 13 17;
2 26 4 29 22 9 5 29 1;
19 11 21 12 7 24 20 12 16;
% ... many rows like this ...
13 21 11 18 25 6 10 18 14]+1;
What is the semantic meaning of the +1 at the end of the array declaration?
Simply adding 1 to each entry:
>> [1 2 3; 4 5 6]
ans =
1 2 3
4 5 6
>> [1 2 3; 4 5 6] + 1
ans =
2 3 4
5 6 7
If you have MATLAB around, you could have figured that out by just trying. If you do not, I hope you have a very clear picture of what the code is doing and write a good test suite, since you won't be able to compare your new code's output to the MATLAB one.
The +1 means that all elements of the written matrix will be increased by one.
Example
out = [1 2;
3 4] + 1;
disp(out)
2 3
4 5
I have a 1 x 15 array of values:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
I need to rearrange them into a 3 x 5 matrix using a for loop:
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
How would I do that?
I'm going to show you three methods. One where you need to have a for loop, and two others when you don't:
Method #1 - for loop
First, create a matrix that is 3 x 5, then keep track of an index that will go through your array. After, create a double for loop that will help you populate the array.
index = 1;
array = 1 : 15; %// Array we wish to access
matrix = zeros(3,5); %// Initialize
for m = 1 : 3
for n = 1 : 5
matrix(m,n) = array(index);
index = index + 1;
end
end
matrix =
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
Method #2 - Without a for loop
Simply put, use reshape:
matrix = reshape(1:15, 5, 3).';
matrix =
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
reshape will take a vector and restructure it into a matrix so that you populate the matrix by columns first. As such, we want to put 1 to 5 in the first column, 6 to 10 in the second and 11 to 15 in the third column. Therefore, our output matrix is in fact 5 x 3. When you see this, this is actually the transposed version of the matrix we want, which is why you do .' to transpose the matrix back.
Method #3 - Another method without a for loop (tip of the hat goes to Luis Mendo)
You can use vec2mat, and specify that you need to have 5 columns worth for your matrix:
matrix = vec2mat(1:15, 5);
matrix =
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
vec2mat takes a vector and reshapes it into a matrix of as many columns as you specify in the second parameter. In this case, we need 5 columns.
For the sake of (bsx)fun, here is another option...
bsxfun(#plus,1:5,[0:5:10]')
ans =
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
less readable, maybe faster, but who cares if it is such a small of an array...
A = [ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ] ;
A = reshape( A' , 3 , 5 ) ;
A' = 1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
I have the following example dataset which consists of the # of fish caught per check of a net. The nets are not checked at uniform intervals. The day of the check is denoted in julian days as well as the number of days the net had been fishing since last checked (or since it's deployment in the case of the first check)
http://textuploader.com/9ybp
Site_Number Check_Day_Julian Set_Duration_Days Fish_Caught
2 5 3 100
2 10 5 70
2 12 2 65
2 15 3 22
100 4 3 45
100 10 6 20
100 18 8 8
450 10 10 10
450 14 4 4
In any case, I would like to turn the raw data above into the following format:
http://textuploader.com/9y3t
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
2 0 0 100 100 100 70 70 70 70 70 65 65 22 22 22 0 0 0
100 0 45 45 45 20 20 20 20 20 20 8 8 8 8 8 8 8 8
450 10 10 10 10 10 10 10 10 10 10 4 4 4 4 0 0 0 0
This is a matrix which assigns the # of fish caught during the period to EACH of the days that were within that period. The columns of the matrix are Julian days, the rows are site numbers.
I have tried to do this with some matrix functions but I have had much difficulty trying to populate all the fields that are within the time period, but I do not necessarily have a row of data for?
I had posted my small bit of code here, but upon reflection, my approach is quite archaic and a bit off point. Can anyone suggest a method to convert the data into the matrix provided? I've been scratching my head and googling all day but now I am stumped.
Cheers,
C
Two answers, the second one is faster but a bit low level.
Solution #1:
library(IRanges)
with(d, {
ir <- IRanges(end=Check_Day_Julian, width=Set_Duration_Days)
cov <- coverage(split(ir, Site_Number),
weight=split(Fish_Caught, Site_Number),
width=max(end(ir)))
do.call(rbind, lapply(cov, as.vector))
})
Solution #2:
with(d, {
ir <- IRanges(end=Check_Day_Julian, width=Set_Duration_Days)
site <- factor(Site_Number, unique(Site_Number))
m <- matrix(0, length(levels(site)), max(end(ir)))
ind <- cbind(rep(site, width(ir)), as.integer(ir))
m[ind] <- rep(Fish_Caught, width(ir))
m
})
I don't see a super obvious matrix transformation here. This is all i've got assuming the raw data is in a data.frame called dd
dd$Site_Number<-factor(dd$Site_Number)
mm<-matrix(0, nrow=nlevels(dd$Site_Number), ncol=18)
for(i in 1:nrow(dd)) {
mm[as.numeric(dd[i,1]), (dd[i,2]-dd[i,3]):dd[i,2] ] <- dd[i,4]
}
mm