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back to boardShow all messages Hide all messagesI always have WA.
The idea is simple: get derivative from distance.
assume a1=x[i]-x[j],a2=y[i]-y[j],a3=z[i]-z[j], b1 = vx[i]-vx[j],b2 = vy[i]-vy[j],b3 = vz[i]-vz[j].
Then we should solve quadric equation ax^2+bx+c to find time, where a=a = (b1*b1+b2*b2+b3*b3), b = 2*(a1*b1+a2*b2+a3*b3), c = (a1*a1+a2*a2+a3*a3)-d;
where i'm wrong?
Edited by author 02.03.2008 22:32 it's right
if d = d * d
check negative roots
be careful with float point
try this random test
4 15.0
15.0 1.4 -3.0 3.0 54.0 130.0
65.0 23.0 4.0 5.0 3.0 34.4
23.0 57.0 5.0 8.0 4.0 31.4
7.0 34.0 7.0 123.0 76.0 54.4
ALARM!
0.124 3 4
Edited by author 03.03.2008 04:35
Edited by author 03.03.2008 04:36 Please give me tests when the roots are negative!! it's not hard
2 0.1
0 1 0 1 1 0
0 0 0 1 -1 0
OK
roots -0.45 and -0.55
one more test(with positive roots)
2 0.1
-10000 -10000 0 0.1 0.1 0
-10000 10000 0 0.1 0 0
ALARM!
199999.000 1 2 Why we should check negative roots if d = d*d ???
what happen when d==d*d??
Edited by author 04.03.2008 17:24 Why we should check negative roots if d = d*d ???
Edited by author 04.03.2008 17:24 it's right if d = d * d , :) check negative roots what happen when d==d*d?? nothing! I just wanted to say that we should replace d with d*d before calculations Edited by author 04.03.2008 19:51If I`m not mistaken, x in equation ax^2+bx+c is time from the begging...so we shouldn`t check negative roots, because it was before the start point!
What`s wrong? I can`t understand... If I`m not mistaken, x in equation ax^2+bx+c is time from the begging...so we shouldn`t check negative roots, because it was before the start point!
What`s wrong? I can`t understand... in this case check == ignore we chose smallest positive root you can send me your code I'll check it in this case check != ignore :) Please, give me some hints related to
"be careful with float point"? use eps
for example
if (discriminant<0) continue; // it's wrong
if (discriminant+1e-9<0) continue; // it's right
Edited by author 06.03.2008 20:41 Thank you! I used
#define EPS 0.000000001
if(discr>=-EPS)
and had got AC!
Edited by author 03.03.2008 23:43
Edited by author 03.03.2008 23:43 I always have WA.
The idea is simple: get derivative from distance.
assume a1=x[i]-x[j],a2=y[i]-y[j],a3=z[i]-z[j], b1 = vx[i]-vx[j],b2 = vy[i]-vy[j],b3 = vz[i]-vz[j].
Then we should solve quadric equation ax^2+bx+c to find time, where a=a = (b1*b1+b2*b2+b3*b3), b = 2*(a1*b1+a2*b2+a3*b3), c = (a1*a1+a2*a2+a3*a3)-d;
where i'm wrong?
Edited by author 02.03.2008 22:32 Don't use this formula. It's not right. Silly author mistake =) |
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