I have a question on this code.
It's the code for finding delay.
in order to estimate the delay,
in my mind,I should find the largest value from the array mean_bit_counts[], but in the picture, they choose the smallest one. So could you solve my problem? Thanks!
// Find |candidate_delay|, |value_best_candidate| and |value_worst_candidate|
// of |mean_bit_counts|.
for (i = 0; i < self->history_size; i++) {
if (self->mean_bit_counts[i] < value_best_candidate) {
value_best_candidate = self->mean_bit_counts[I];
candidate_delay = I;
}
if (self->mean_bit_counts[i] > value_worst_candidate) {
value_worst_candidate = self->mean_bit_counts[I];
}
}
valley_depth = value_worst_candidate - value_best_candidate;
Related
Could anyone explain me the time complexity of this method?
int sqrt = (int) Math.sqrt(n) + 1;
for (int i = 2; i < sqrt; i++) {
if (n % i == 0) {
return false;
}
}
return true;
I'm not really good in this subject and tried to find out some info online but could't find any explanation.
its On(1) - linear, as it its linearly proportional on i (or less due to early stopping from module check); this is typical for a one level for loop
I am learning p5.js and wanted to generate a "static/noise texture" like so:
This is the code:
for (let y = 0; y < height; y++) {
for (let x = 0; x < width; x++) {
noiseVal = random(0,1);
stroke(255, noiseVal*255);
point(x,y);
}
}
This produces the desired outcome but it's obviously pretty slow since it has to iterate over every single pixel. What would be a more efficient way of doing this?
Your code is really not the best way to do with p5.js.
Take a look to the p5's pixels array.
When I run the following code, the function that use the pixels array run 100 times faster.
function setup() {
createCanvas(50, 50);
background(255);
let start, time;
start = performance.now();
noise_1();
time = performance.now() - start;
print("noise_1 : " + time);
start = performance.now();
noise_2();
time = performance.now() -start;
print("noise_2 : " + time);
}
// Your code
function noise_1() {
for (let y = 0; y < height; y++) {
for (let x = 0; x < width; x++) {
noiseVal = random(0,1);
stroke(noiseVal*255);
point(x,y);
}
}
}
// same with pixels array
function noise_2() {
loadPixels();
for (let i=0; i < pixels.length; i+=4){
noiseVal = random(0, 255);
pixels[i] = pixels[i+1] = pixels[i+2] = noiseVal;
}
updatePixels();
}
output :
noise_1 : 495.1
noise_2 : 5.92
To generate a single frame of static, you're going to have to iterate over each pixel. You could make your blocks larger than a single pixel, but that will only reduce the problem, not get rid of it completely.
Instead, you can probably get away with pre-computing a few images of static (let's say 10 or so). Save these as a file or to an off-screen buffer (the createGraphics() function is your friend), and then draw those images instead of drawing each pixel every frame.
I a writing a program using RobotC for the Lego NXT to imitate the behaviour of a puppy. This section of code is supposed to rotate the head which is connected to motor port 3 and read the value on the ultra sonic sensor. If while the head is turned, the dog is called, it will turn in the direction it was already facing. The following function is called when the ultrasonic sensor reads a value (meaning the robot has come close to a wall):
visible
void SonarSensor()
{
int sensorValleft;
int sensorValright;
bool alreadyTurned = false;
int i,j;
i = 0;
j = 0;
motor[1] = 0;
motor[2] = 0;
motor[3] = -SPEED/2;
wait10Msec(15);
motor[3] = 0;
sensorValleft = SensorValue[3];
while(i<100)
{
if(SensorValue[4] > 40)//calibrate sound sensor
{
//turn left
motor[1]=SPEED;
motor[2] = -SPEED;
wait10Msec(25);
i = 1000;
j = 1000;
alreadyTurned = true;
}
else
{
i++;
wait1Msec(5);
}
}
motor[3] = SPEED/2;
wait10Msec(30);
motor[3] = 0;
sensorValright = SensorValue[3];
while(j<100)
{
if(SensorValue[3] > 1)//calibrate sound sensor
{
//turn right
motor[1]-=SPEED;
motor[2] = SPEED;
wait10Msec(25);
j = 1000;
alreadyTurned = true;
}
else
{
j++;
wait1Msec(5);
}
}
if(alreadyTurned == false)
{
if(sensorValleft > sensorValright)
{
//turn left
motor[1]=SPEED;
motor[2] = -SPEED;
wait10Msec(25);
}
else
{
//turn right
motor[1]=-SPEED;
motor[2] = SPEED;
wait10Msec(25);
}
}
}visible
When the head (motor[3]) rotates the first time the error 0002EA Type2 appears on the NXT screen. At first we thought it was because we were over-rotating the motor causing it to be obstructed so we tried to play around with the wait times but it made no difference.
Any ideas on what causes this error or how to fix it would be appreciated.
Thanks,
Dominique
The answer as to why only motor[3] causes an error is actually quite simple. The motorA, motorB, and motorC values are defined in an enum, where motorA=0, motorB=1, and motorC=2. So, motor[1] and motor[2] are equivalent to calling motor[motorB] and motor[motorC]. However, motor[3] isn't equivalent to anything. It's trying to set the power of a motor that doesn't exist. motor[0] would be ok, however, and would correspond to motor[motorA].
While debugging, I started putting break points in to see where the error was and it alwas occurred on the line motor[3] = -SPEED/2; it turns out that with the third motor the proper syntax is to use motor[motorA]=-SPEED/2;. I am not sure why only this motor returns this error as I am using two other motors which I set new speeds using
motor[1]=SPEED;
motor[2]=SPEED;
However, this was the way to abolish the error.
I have some script that is delivering a series of rows from an SQL database.
I want to append.() a button to each row. My current code is:
tx.executeSql('SELECT * FROM myprogram', [], function (tx, results) {
var len = results.rows.length, i;
for (i = 0; i < len; i++) {
$('#myprog').append(results.rows.item(i).event)
$('.event').append('<button class="save_event">Remove</button>');
}
});
But the buttons get doubled up. For example if I get 3 rows, the first row will have 3 buttons, the 2nd will have 2 and the last will have 1 button.
Can anyone help me out to have the buttons display only once per row?
Thanks!
I found the answer, quite simple:
var len = results.rows.length, i;
for (i = 0; i < len; i++) {
$('#myprog').append(results.rows.item(i).event).append('<button class="remove_event">Remove</button>');
}
$('#myprog').append(results.rows.item(i).event).append('<button class="remove_event">Remove</button>');
You need to append to $('#myprog') selector.
I brute-forced summing of all primes under 2000000. After that, just for fun I tried to parallel my for, but I was a little bit surprised when I saw that Parallel.For gives me an incorrect sum!
Here's my code : (C#)
static class Problem
{
public static long Solution()
{
long sum = 0;
//Correct result is 142913828922
//Parallel.For(2, 2000000, i =>
// {
// if (IsPrime(i)) sum += i;
// });
for (int i = 2; i < 2000000; i++)
{
if (IsPrime(i)) sum += i;
}
return sum;
}
private static bool IsPrime(int value)
{
for (int i = 2; i <= (int)Math.Sqrt(value); i++)
{
if (value % i == 0) return false;
}
return true;
}
}
I know that brute-force is pretty bad solution here but that is not a question about that. I think I've made some very stupid mistake, but I just can't locate it. So, for is calculating correctly, but Parallel.For is not.
You are accessing the variable sum from multiple threads without locking it, so it is possible that the read / write operations become overlapped.
Adding a lock will correct the result (but you will be effectively serializing the computation, losing the benefit you were aiming for).
You should instead calculate a subtotal on each thread and add the sub-totals at the end. See the article How to: Write a Parallel.For Loop That Has Thread-Local Variables on MSDN for more details.
long total = 0;
// Use type parameter to make subtotal a long, not an int
Parallel.For<long>(0, nums.Length, () => 0, (j, loop, subtotal) =>
{
subtotal += nums[j];
return subtotal;
},
(x) => Interlocked.Add(ref total, x)
);
Many thanks to all of you for your quick answers
i changed
sum += i;
to
Interlocked.Add(ref sum,i);
and now it works great.