peculiarity about creating a file using output redirection and opening a file with cat - system-calls
I noticed that creating a file using output redirection involves neither creat() or open() system call. I thinks this is due to the stdin and stdout always exist and are always open. But how can I detect (i.e., using dtrace) file creation/read/write in those case?
Please see below turss outputs.
echo 888 >/var/tmp/testfile1
7570/1: 0.0022 0.0022 0.0000 sysinfo(SI_MACHINE, "i86pc", 257) = 6
7570/1: 0.0022 0.0000 0.0000 mmap(0x00000000, 32, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANON, -1, 0) = 0xFEFF0000
7570/1: 0.0023 0.0001 0.0000 mmap(0x00000000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0) = 0xFEFB0000
7570/1: 0.0024 0.0001 0.0000 mmap(0x00000000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0) = 0xFEFA0000
7570/1: 0.0024 0.0000 0.0000 memcntl(0xFEFBE000, 13608, MC_ADVISE, MADV_WILLNEED, 0, 0) = 0
7570/1: 0.0025 0.0001 0.0000 mmap(0x00000000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANON, -1, 0) = 0xFEF90000
7570/1: 0.0025 0.0000 0.0000 memcntl(0x08050000, 1708, MC_ADVISE, MADV_WILLNEED, 0, 0) = 0
7570/1: 0.0026 0.0001 0.0000 resolvepath("/usr/lib/ld.so.1", "/lib/ld.so.1", 1023) = 12
7570/1: 0.0027 0.0001 0.0000 resolvepath("/usr/bin/echo", "/usr/bin/echo", 1023) = 13
7570/1: 0.0027 0.0000 0.0000 sysconfig(_CONFIG_PAGESIZE) = 4096
7570/1: 0.0028 0.0001 0.0000 stat64("/usr/bin/echo", 0x08045C10) = 0
7570/1: 0.0028 0.0000 0.0000 open("/var/ld/ld.config", O_RDONLY) Err#2 ENOENT
7570/1: 0.0029 0.0001 0.0000 stat64("/usr/lib/libc.so.1", 0x080454C0) = 0
7570/1: 0.0030 0.0001 0.0000 resolvepath("/usr/lib/libc.so.1", "/lib/libc.so.1", 1023) = 14
7570/1: 0.0030 0.0000 0.0000 open("/usr/lib/libc.so.1", O_RDONLY) = 3
7570/1: 0.0031 0.0001 0.0000 mmap(0x00010000, 32768, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_ALIGN, 3, 0) = 0xFEF80000
7570/1: 0.0031 0.0000 0.0000 mmap(0x00010000, 1155072, PROT_NONE, MAP_PRIVATE|MAP_NORESERVE|MAP_ANON|MAP_ALIGN, -1, 0) = 0xFEE60000
7570/1: 0.0032 0.0001 0.0000 mmap(0xFEE60000, 1110613, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_TEXT, 3, 0) = 0xFEE60000
7570/1: 0.0032 0.0000 0.0000 mmap(0xFEF70000, 30255, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_INITDATA, 3, 1114112) = 0xFEF70000
7570/1: 0.0033 0.0001 0.0000 mmap(0xFEF78000, 4200, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_ANON, -1, 0) = 0xFEF78000
7570/1: 0.0033 0.0000 0.0000 munmap(0xFEF80000, 32768) = 0
7570/1: 0.0034 0.0001 0.0000 close(3) = 0
7570/1: 0.0034 0.0000 0.0000 mmap(0x00000000, 12288, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANON, -1, 0) = 0xFEF80000
7570/1: 0.0035 0.0001 0.0000 memcntl(0xFEE60000, 124760, MC_ADVISE, MADV_WILLNEED, 0, 0) = 0
7570/1: 0.0038 0.0003 0.0000 mmap(0x00010000, 24576, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANON|MAP_ALIGN, -1, 0) = 0xFEE50000
7570/1: 0.0039 0.0001 0.0000 getcontext(0x08045A80)
7570/1: 0.0039 0.0000 0.0000 getrlimit(RLIMIT_STACK, 0x08045A78) = 0
7570/1: 0.0039 0.0000 0.0000 getpid() = 7570 [7569]
7570/1: 0.0040 0.0001 0.0000 lwp_private(0, 1, 0xFEE52A00) = 0x000001C3
7570/1: 0.0041 0.0001 0.0000 setustack(0xFEE52A60)
7570/1: 0.0041 0.0000 0.0000 sysi86(SI86FPSTART, 0xFEF78718, 0x0000133F, 0x00001F80) = 0x00000001
7570/1: 0.0042 0.0001 0.0000 ioctl(1, TCGETA, 0x08045E64) Err#25 ENOTTY
7570/1: 0.0043 0.0001 0.0000 fstat64(1, 0x08045E90) = 0
7570/1: 0.0042 0.0001 0.0000 ioctl(1, TCGETA, 0x08045E64) Err#25 ENOTTY
7570/1: 0.0043 0.0001 0.0000 fstat64(1, 0x08045E90) = 0
7570/1: 0.0043 0.0000 0.0000 brk(0x08061710) = 0
7570/1: 0.0044 0.0001 0.0000 brk(0x08083710) = 0
7570/1: 0.0044 0.0000 0.0000 fstat64(1, 0x08045DD0) = 0
7570/1: 0.0045 0.0001 0.0000 write(1, " 8 8 8\n", 4) = 4
7570/1: 0.0046 0.0001 0.0000 _exit(0)
Redirection is done by your shell, not the echo command. echo just outputs to the standard output (descriptor 1), which your shell made point to /var/tmp/testfile1. Try strace -ff sh -c "echo > /tmp/somefile" and you'll see /tmp/somefile is being open for writing.
You missed the open64 function
Related
continuous wavelet transfrom of a signal
I want to carry out continuous wavelet transform of a signal. I tried to write a script but the script give output of very low resolution scalogram. So I need a high resolution output by changing some scales. The signal data and the script is attached below.
I tried the script
from scipy import signal
import numpy as np
import matplotlib.pyplot as plt
import obspy
w=np.loadtxt('signal')
t = np.arange(0,len(w))
fmin = 1 # Hz
fmax = 50 # Hz
df = 1./(t[-1]-t[0])
print(df)
fmin_samples = int(fmin/df)
fmax_samples = int(fmax/df)
extent = np.arange(1,10)
scalogram = signal.cwt(w, signal.morlet,extent)
fig, ax = plt.subplots(2, 1, sharex=True)
ax[0].plot(t, w)
ax[0].set(ylabel='amplitude')
ax[1].imshow(np.abs(scalogram), origin='lower')
ax[1].axis('tight')
ax[1].set(xlabel='time (s)', ylabel='frequency (Hz)')
plt.show()
signal data
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0000
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0001
-0.0002
-0.0002
-0.0002
-0.0002
-0.0002
-0.0002
-0.0002
-0.0002
-0.0002
-0.0003
-0.0003
-0.0003
-0.0003
-0.0003
-0.0004
-0.0004
-0.0004
-0.0004
-0.0005
-0.0005
-0.0006
-0.0006
-0.0007
-0.0007
-0.0008
-0.0009
-0.0009
-0.0010
-0.0011
-0.0013
-0.0014
-0.0015
-0.0017
-0.0019
-0.0022
-0.0025
-0.0028
-0.0032
-0.0037
-0.0043
-0.0051
-0.0060
-0.0072
-0.0087
-0.0108
-0.0136
-0.0178
-0.0241
-0.0338
-0.0493
-0.0724
-0.1014
-0.1231
-0.1059
-0.0038
0.2143
0.5147
0.7698
0.8049
0.5211
-0.0000
-0.5212
-0.8050
-0.7698
-0.5148
-0.2144
0.0038
0.1059
0.1231
0.1013
0.0725
0.0492
0.0340
0.0240
0.0174
0.0136
0.0106
0.0086
0.0070
0.0059
0.0049
0.0042
0.0036
0.0031
0.0026
0.0023
0.0020
0.0018
0.0015
0.0014
0.0012
0.0010
0.0009
0.0008
0.0007
0.0006
0.0005
0.0004
0.0003
0.0003
0.0002
0.0001
0.0000
-0.0000
-0.0001
-0.0002
-0.0003
-0.0004
-0.0005
-0.0006
-0.0007
-0.0008
-0.0010
-0.0011
-0.0013
-0.0015
-0.0018
-0.0020
-0.0024
-0.0028
-0.0034
-0.0040
-0.0049
-0.0060
-0.0074
-0.0094
-0.0123
-0.0167
-0.0235
-0.0344
-0.0506
-0.0709
-0.0861
-0.0740
-0.0026
0.1501
0.3604
0.5389
0.5635
0.3649
0.0001
-0.3648
-0.5634
-0.5388
-0.3603
-0.1500
0.0027
0.0742
0.0862
0.0710
0.0508
0.0345
0.0239
0.0169
0.0123
0.0096
0.0075
0.0062
0.0050
0.0042
0.0035
0.0030
0.0026
0.0023
0.0020
0.0017
0.0015
0.0014
0.0012
0.0011
0.0010
0.0009
0.0008
0.0007
0.0007
0.0006
0.0006
0.0005
0.0005
0.0004
0.0004
0.0004
0.0003
0.0003
0.0003
0.0003
0.0003
0.0002
0.0002
0.0002
0.0002
0.0002
0.0002
0.0002
0.0002
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0000
0.0000
0.0000
0.0000
0.0000
Using a library named PyWavelets (documentation here) you can do it in a straightforward way
import pywt
import pylab
[phi, psi, x] = pywt.Wavelet('db2').wavefun(level=4)
pylab.plot(x, psi)
pylab.show()
How to vectorize this code involving matrix pages in MATLAB?
Is it possible to vectorize, and possibly run on a GPU, the following code x = linspace(0,100,1000); h = zeros(size(x)); for i = 1 : length(x) exprho = expm(-x(i)*rho); h(i) = trace(drho*exprho*drho*exprho); end out = 2 * trapz(x,h); where rho and drho are two complex Hermitian square matrices of the same size. rho is in fact a quantum density matrix and drho is its derivative with respect to a parameter. The size can range from 10 x 10 to 300 x 300 approximately but I would also like to reach bigger sizes. Here are two sample matrices: rho = 0.4046 0.3849 0.2589 0.1422 0.0676 0.0288 0.0112 0.0040 0.0014 0.0004 0.0001 0.3849 0.3661 0.2462 0.1352 0.0643 0.0274 0.0106 0.0038 0.0013 0.0004 0.0001 0.2589 0.2462 0.1656 0.0910 0.0433 0.0184 0.0071 0.0026 0.0009 0.0003 0.0001 0.1422 0.1352 0.0910 0.0500 0.0238 0.0101 0.0039 0.0014 0.0005 0.0002 0.0000 0.0676 0.0643 0.0433 0.0238 0.0113 0.0048 0.0019 0.0007 0.0002 0.0001 0.0000 0.0288 0.0274 0.0184 0.0101 0.0048 0.0020 0.0008 0.0003 0.0001 0.0000 0.0000 0.0112 0.0106 0.0071 0.0039 0.0019 0.0008 0.0003 0.0001 0.0000 0.0000 0.0000 0.0040 0.0038 0.0026 0.0014 0.0007 0.0003 0.0001 0.0000 0.0000 0.0000 0.0000 0.0014 0.0013 0.0009 0.0005 0.0002 0.0001 0.0000 0.0000 0.0000 0.0000 0.0000 0.0004 0.0004 0.0003 0.0002 0.0001 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0001 0.0001 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 drho = 0.0366 0.0156 -0.0025 -0.0085 -0.0074 -0.0046 -0.0023 -0.0010 -0.0004 -0.0002 -0.0001 0.0156 -0.0035 -0.0147 -0.0148 -0.0103 -0.0057 -0.0028 -0.0012 -0.0005 -0.0002 -0.0001 -0.0025 -0.0147 -0.0181 -0.0145 -0.0091 -0.0048 -0.0022 -0.0009 -0.0004 -0.0001 -0.0000 -0.0085 -0.0148 -0.0145 -0.0105 -0.0062 -0.0031 -0.0014 -0.0006 -0.0002 -0.0001 -0.0000 -0.0074 -0.0103 -0.0091 -0.0062 -0.0035 -0.0017 -0.0008 -0.0003 -0.0001 -0.0000 -0.0000 -0.0046 -0.0057 -0.0048 -0.0031 -0.0017 -0.0008 -0.0004 -0.0001 -0.0001 -0.0000 -0.0000 -0.0023 -0.0028 -0.0022 -0.0014 -0.0008 -0.0004 -0.0002 -0.0001 -0.0000 -0.0000 -0.0000 -0.0010 -0.0012 -0.0009 -0.0006 -0.0003 -0.0001 -0.0001 -0.0000 -0.0000 -0.0000 -0.0000 -0.0004 -0.0005 -0.0004 -0.0002 -0.0001 -0.0001 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0002 -0.0002 -0.0001 -0.0001 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0001 -0.0001 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000
Why am I getting a matrix of zeros and infs when dividing matrices of the same dimension by element?
I'm trying to get two matrices to divide, properly, element by element. Essentially, firstd is a 6x499 and secd is 6x498. I first eliminate firstd's extra elements by doing firstd(:,499)=[]; making it 6x498. Now the next step is to transform firstd into the nominator, nom=((firstd.^2)+1).^1.5; My denominator is just denom=secd; Both nom and denom have come out as 6x498 matrices with real, non-zero data for each element. However, when doing Rlayer=nom./denom, Rlayer comes out as this ludicrous 6x498 zero-ridden matrix. I also trimmed out the elements in denom that were =0 by changing them to 0.0001. Segment of result for Rlayer (Columns 493 through 498) -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 0.0000 -0.0000 -0.0000 0.0000 -0.0000 0.0000 0.0000 -0.0000 -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 -0.0000 0.0000 0.0000 -0.0000 Below are two segments of denom (Columns 487 through 492) 0.0250 0.0281 -0.0281 0.0125 -0.0500 0.0969 -0.0125 0.0750 -0.1219 0.1094 -0.0938 0.0937 0.0344 0.0406 -0.1094 0.1187 -0.1344 0.1531 0.0001 0.0250 0.0001 -0.0437 0.0500 0.0062 0.0781 -0.0219 0.0094 -0.0125 -0.0188 0.1062 0.0250 0.0438 -0.0812 0.0937 -0.1063 0.1562 (Columns 493 through 498) -0.1187 0.1156 -0.0844 0.0688 -0.0406 0.0125 -0.0969 0.1094 -0.0906 0.0469 0.0062 -0.0156 -0.1375 0.1719 -0.1656 0.0781 0.0187 -0.0531 -0.0562 0.1188 -0.1500 0.1438 -0.1187 0.1187 -0.1781 0.2281 -0.2156 0.1750 -0.1250 0.0812 -0.1750 0.1938 -0.1469 0.0563 0.0031 -0.0156 and this is a segment of nom (Columns 493 through 498) 1.0904 1.0235 1.0881 1.0368 1.0769 1.0514 1.0685 1.0201 1.0769 1.0272 1.0497 1.0532 1.0928 1.0180 1.1210 1.0201 1.0568 1.0685 1.0568 1.0285 1.1001 1.0170 1.0952 1.0260 1.0952 1.0078 1.1380 1.0107 1.1026 1.0272 1.0928 1.0078 1.1077 1.0212 1.0463 1.0480 Why is this division leading to this result? I've tried dividing with rdivide, in a double for loop, and row by row in a for loop. All number types are double.
Powers Table MATLAB
For this question, I'm supposed to create a NxN powers table in matlab using arrays.
The code I have so far is as follows:
C = [];
D = [];
N = input('Enter the value you would like to use for your NxN Powers Table: ');
for i = 1:N
for j = 1:N
C = [C;i^j];
end
C = transpose(C);
D = [D;C];
C = [];
end
D
This code works perfectly fine for any numbers from 1-9, as soon as I enter anything greater than that, it prints out weird values.
Here is the output I have using 5 as an input, and the second one is using 10 as an input.
Enter the value you would like to use for your NxN Powers Table: 5
D =
1 1 1 1 1
2 4 8 16 32
3 9 27 81 243
4 16 64 256 1024
5 25 125 625 3125
Enter the value you would like to use for your NxN Powers Table: 10
D =
1.0e+010 *
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0002 0.0010
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0002 0.0010 0.0060
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0006 0.0040 0.0282
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0002 0.0017 0.0134 0.1074
0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0005 0.0043 0.0387 0.3487
0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0010 0.0100 0.1000 1.0000
Any ideas what could be wrong with my code? Seems like a simple fix, I just can't figure out whats wrong with it. Any help is greatly appreciated. Thanks
Notice the 1.0e+010 *. It means that the numbers should be multiplied by 10000000000. Five digits are not enough to print it. Insert format long or format short g to see the whole numbers.
I think your code works fine. Note that 10^10 = 1e10; the very last element in your output D is indeed 1e10. Check individual elements D(i,j) to verify that those are correct. MATLAB can't display all the elements because some elements are so much larger than other ones; 1e10 has 10 digits in it, for instance, while 1^1 = 1 has 1 digit. So spacing would get screwed up if this behavior didn't happen.
Matrix creation MATLAB
I am building a nxn matrix in matlab with the following code: x = linspace(a,b,n); for i=1:n for j=1:n A(i,j) = x(j)^(i-1); end A i b(i) = (1/i)*x(n)^i - (1/i)*x(1)^i; end I am testing it with a=1 b=10 and n=10. I get the expected results up to i=8 i = 8 A = Columns 1 through 7 1 1 1 1 1 1 1 1 2 3 4 5 6 7 1 4 9 16 25 36 49 1 8 27 64 125 216 343 1 16 81 256 625 1296 2401 1 32 243 1024 3125 7776 16807 1 64 729 4096 15625 46656 117649 1 128 2187 16384 78125 279936 823543 1 256 6561 65536 390625 1679616 5764801 Columns 8 through 10 1 1 1 8 9 10 64 81 100 512 729 1000 4096 6561 10000 32768 59049 100000 262144 531441 1000000 2097152 4782969 10000000 16777216 43046721 100000000 however from i=9 on it becomes this: i = 9 A = 1.0e+09 * Columns 1 through 9 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0003 0.0005 0.0000 0.0000 0.0000 0.0000 0.0001 0.0003 0.0008 0.0021 0.0048 0.0000 0.0000 0.0000 0.0001 0.0004 0.0017 0.0058 0.0168 0.0430 0.0000 0.0000 0.0000 0.0003 0.0020 0.0101 0.0404 0.1342 0.3874 Column 10 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0010 0.0100 0.1000 1.0000 Can someone please tell me what is happening? I am not very experienced in matlab (I mostly use c++ or python) and so far can't seem to figure it out myself.
It's just a formatting issue for larger numbers. Try
sprintf('%20.0f', A(end,end))
and you will see that the number is correct. At least up to some point, where you will run into double representation problems...
Because a common scaling is applied to your data display. See in your output: A = 1.0e+09 * A common factor of 10^9 was factored out of every entry in your matrix. You may want to adjust your output display using: format short g