Unable to open a tar.gz file

Question

I'm writing a Metropolis-Hastings algorithm for a N(0,1) distribution:

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
NumericVector metropolis(int R, double b, double x0){
    NumericVector y(R);
    y(1) = x0;
    for(int i=1; i<R; ++i){
       y(i) = y(i-1);
       double xs = y(i)+runif(1, -b,b)[0];
       double a = dnorm(xs, 0, 1)[0]/dnorm(y(i), 0, 1)[0];
       NumericVector A(2);
       A(0) = 1;
       A(1) = a;
       double random = runif(1)[0];
       if(random <= min(A)){
            y[i] = xs;
       }
   }
   return y;
}

but every time I try to compile the function, this error occurs:

Line 12: no matching function for call to 'dnorm4'

I tried to write a trivial function using dnorm, like

NumericVector den(NumericVector y, double a, double b){
    NumericVector x = dnorm(y,a,b);
    return x;
}

and it works. Does someone know why I have this type of error in the Metropolis code? Are there some other ways to use density functions in the C++ code like in R?

Solution 1

I would guess that the archive is damaged. Try downloading it again, and even controlling the checksum if an intended value is given at the download site if it does not work.

If it still does not work, try

gunzip mysql-5.1.33.tar.gz

to see if the compression is done correctly, and then

tar xvf mysql-5.1.33.tar

to try to unroll the archive. This will pin point the problem better.

Solution 2

I had the same problem and it turned out that when I had downloaded the .tar.gz file, I had clicked "Download Link" on a page that led to a second page with the actual download.

So, my .tar.gz was just a bunch of HTML.

You can check by posting the address of the .tar.gz in your browser to make sure it's an actual compressed file.

Comments

[Mike Purcell]

Try just unzipping it first, and ensure it's a valid tar file.

[Admin]

This isn't a suitable question for stackoverflow. Perhaps unix.stackexchange.com. While you're here, what does 'file' tell you about the archive?

[hkf]

unzip with gzip first, then use tar.

[Dirk Eddelbuettel]

There are dozens of suitable examples on the Rcpp Gallery, here on SO and other places.

[stafffan]

Thanks for this idea. My problem was that the actual file (that I'd tried to curl) didn't exist anymore, so my tar file was actually a 404 page.

[Dirk Eddelbuettel]

There is also the unaltered interface to R's Rf_* functions to I count three. All this has been discussed at length here and on other places. Really no need for a new question, but a fine answer. Thanks, @coatless.