### Author:  [@bdeonovic](https://discourse.julialang.org/u/bdeonovic)
#### Post date: [February 24, 2017, 9:59pm UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/1 "2017-02-24T21:59:08Z")
Trying to call a fortran function. The fortran library is [qrupdate](https://sourceforge.net/projects/qrupdate/). The fortran files were compiled with flags
> -fimplicit-none -O3 -funroll-loops -fPIC
using `gfortran`.
My julia command looks like
```julia
ccall(("sqrinr_","qrupdate-1.1.2/libqrupdate"), Int32, (Int64, Int64, Array{Float64, 2}, Int64, Array{Float64, 2}, Int64, Int64, Array{Float64, 1}, Array{Float64, 1}), n, q, Q, n+1, R, n+1, n, xp, w)
```
and I get a segfault
```julia
signal (11): Segmentation fault
while loading no file, in expression starting on line 0
sqrinr_ at qrupdate-1.1.2/libqrupdate.so (unknown line)
anonymous at ./ (unknown line)
unknown function (ip: 0x7f084dec901f)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_toplevel_eval_flex at /home/centos/buildbot/slave/package_tarball64/build/src/toplevel.c:569 [inlined]
jl_toplevel_eval at /home/centos/buildbot/slave/package_tarball64/build/src/toplevel.c:580
jl_toplevel_eval_in_warn at /home/centos/buildbot/slave/package_tarball64/build/src/builtins.c:590
eval at ./boot.jl:234
unknown function (ip: 0x7f0a58ebf4df)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
eval_user_input at ./REPL.jl:64
unknown function (ip: 0x7f084de9a0a6)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
macro expansion at ./REPL.jl:95 [inlined]
#3 at ./event.jl:68
unknown function (ip: 0x7f084de971cf)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
jl_apply at /home/centos/buildbot/slave/package_tarball64/build/src/julia.h:1392 [inlined]
start_task at /home/centos/buildbot/slave/package_tarball64/build/src/task.c:253
unknown function (ip: 0xffffffffffffffff)
Allocations: 6546676 (Pool: 6544886; Big: 1790); GC: 10
Segmentation fault
```
I have no idea how to approach the problem, can someone point me in right direction?
---
### Author:  [@rdeits](https://discourse.julialang.org/u/rdeits)
#### Post date: [February 24, 2017, 10:54pm UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/2 "2017-02-24T22:54:55Z")
I don’t have much experience here, but I think the issue is that fortran expects _all_ arguments to be passed by reference (see here: [http://docs.julialang.org/en/stable/manual/calling-c-and-fortran-code/#calling-c-and-fortran-code](http://docs.julialang.org/en/stable/manual/calling-c-and-fortran-code/#calling-c-and-fortran-code) ). There’s a note in the ccall docs that says as much:
> When calling a Fortran function, all inputs must be passed by reference, so all type correspondences above should contain an additional Ptr{…} or Ref{…} wrapper around their type specification.
---
### Author:  [@bdeonovic](https://discourse.julialang.org/u/bdeonovic)
#### Post date: [February 24, 2017, 11:05pm UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/3 "2017-02-24T23:05:36Z")
Thanks I will try that out.
---
### Author:  [@bdeonovic](https://discourse.julialang.org/u/bdeonovic)
#### Post date: [February 25, 2017, 12:37am UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/4 "2017-02-25T00:37:50Z")
I changed the `ccall` to
```julia
julia> ccall(("sqrinr_","qrupdate-1.1.2/libqrupdate"), Void, (Ref{Int64}, Ref{Int64}, Ref{Array{Float64, 2}}, Ref{Int64}, Ref{Array{Float64, 2}}, Ref{Int64}, Ref{Int64}
, Ref{Array{Float64, 1}}, Ref{Array{Float64, 1}}), n, q, Q, n+1, R, n+1, n, xp, w)
```
and it seemed to run without error, but when I look at Q I get a segfault. The fortran function is supposed to modify Q (and R). Any more hints and tips?
```julia
julia> Q
4×1 Array{Float64,2}:
signal (11): Segmentation fault
while loading no file, in expression starting on line 0
jl_array_isassigned at /home/centos/buildbot/slave/package_tarball64/build/src/array.c:487
isassigned at ./array.jl:36
alignment at ./show.jl:1277
unknown function (ip: 0x7f49ad3eeaee)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
print_matrix at ./show.jl:1407
print_matrix at ./show.jl:1379 [32/210]
unknown function (ip: 0x7f49ad3ea366)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
jl_apply at /home/centos/buildbot/slave/package_tarball64/build/src/julia.h:1392 [inlined]
jl_f__apply at /home/centos/buildbot/slave/package_tarball64/build/src/builtins.c:547
#showarray#330 at ./show.jl:1618
unknown function (ip: 0x7f49ad3e517d)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
display at ./REPL.jl:132
unknown function (ip: 0x7f49ad3e4cb6)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
display at ./REPL.jl:135
unknown function (ip: 0x7f49ad3e4986)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
display at ./multimedia.jl:143
unknown function (ip: 0x7f49ad3e47d2)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
print_response at ./REPL.jl:154
unknown function (ip: 0x7f49ad3e3ae8)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942 [7/210]
print_response at ./REPL.jl:139
unknown function (ip: 0x7f49ad3e3568)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
#22 at ./REPL.jl:652
unknown function (ip: 0x7f49ad3e1c81)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
run_interface at ./LineEdit.jl:1579
unknown function (ip: 0x7f4bb84270bf)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
run_frontend at ./REPL.jl:903
run_repl at ./REPL.jl:188
unknown function (ip: 0x7f49ad3df712)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
_start at ./client.jl:360
unknown function (ip: 0x7f4bb84422e8)
jl_call_method_internal at /home/centos/buildbot/slave/package_tarball64/build/src/julia_internal.h:189 [inlined]
jl_apply_generic at /home/centos/buildbot/slave/package_tarball64/build/src/gf.c:1942
jl_apply at /home/centos/buildbot/slave/package_tarball64/build/ui/../src/julia.h:1392 [inlined]
true_main at /home/centos/buildbot/slave/package_tarball64/build/ui/repl.c:112
main at /home/centos/buildbot/slave/package_tarball64/build/ui/repl.c:232
__libc_start_main at /lib64/libc.so.6 (unknown line)
unknown function (ip: 0x4013fc)
Allocations: 7528308 (Pool: 7526481; Big: 1827); GC: 12
Segmentation fault
```
---
### Author:  [@m-j-w](https://discourse.julialang.org/u/m-j-w)
#### Post date: [February 25, 2017, 1:16am UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/5 "2017-02-25T01:16:39Z")
It would be much easier to give advice if you would show the exact Fortran function signature you’re trying to call. Apart from that: an `Array` should already be a pointed to memory block, so no need for the `Ref{...}` - at least as long as it’s not allocatable. You may want to check that you really need `Int64`.
---
### Author:  [@bdeonovic](https://discourse.julialang.org/u/bdeonovic)
#### Post date: [February 25, 2017, 1:24am UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/6 "2017-02-25T01:24:30Z")
The fortran function is
```julia
subroutine sqrinr(m,n,Q,ldq,R,ldr,j,x,w)
c purpose: updates a QR factorization after inserting a new
c row.
c i.e., given an m-by-m unitary matrix Q, an m-by-n
c upper trapezoidal matrix R and index j in the range
c 1:m+1, this subroutine updates Q -> Q1 and R -> R1
c so that Q1 is again unitary, R1 upper trapezoidal,
c and Q1*R1 = [A(1:j-1,:); x; A(j:m,:)], where A = Q*R.
c (real version)
c arguments:
c m (in) number of rows of the matrix Q.
c n (in) number of columns of the matrix R.
c Q (io) on entry, the unitary matrix Q.
c on exit, the updated matrix Q1.
c ldq (in) leading dimension of Q. ldq >= m+1.
c R (io) on entry, the original matrix R.
c on exit, the updated matrix R1.
c ldr (in) leading dimension of R. ldr >= m+1.
c j (in) the position of the new row in R1
c x (io) on entry, the row being added
c on exit, x is destroyed.
c w (out) a workspace vector of size min(m,n).
```
I removed the Ref{…} on the Arrays.
---
### Author:  [@m-j-w](https://discourse.julialang.org/u/m-j-w)
#### Post date: [February 25, 2017, 1:46am UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/7 "2017-02-25T01:46:42Z")
The signature including the types, which is the important information here, is
```julia
subroutine sqrinr(m,n,Q,ldq,R,ldr,j,x,w)
integer m,n,ldq,ldr
real Q(ldq,*),R(ldr,*),x(*),w(*)
end subroutine
```
Since this is Fortran77, and presuming you didn’t give other compiler flags to switch to 64bit default integer and float size, then the ccall should be along the lines of
```julia
Q = zeros( Float32, n+1, q )
R = zeros( Float32, n+1, q )
x = zeros( Float32, n)
w = zeros( Float32, min(n,q))
ccall( ("sqrinr_","qrupdate-1.1.2/libqrupdate")
, Void # nothing returned by Fortran subroutines
, ( Ref{Int32} # m
, Ref{Int32} # n
, Ref{Float32} # Q, not Array{Float32, 2}
, Ref{Int32} # ldq
, Ref{Float32} # R, not Array{Float32, 2}
, Ref{Int32} # ldr
, Ref{Int32} # j
, Ref{Float32} # x, not Array{Float32, 1}
, Ref{Float32} # w, not Array{Float32, 1}
)
, n, q, Q, n+1, R, n+1, n, xp, w)
```
**Edit:** Of course, Simon is correct and the array should also be passed as a `Ref{T}`. Changed the above lines accordingly.
---
### Author:  [@simonbyrne](https://discourse.julialang.org/u/simonbyrne)
#### Post date: [February 25, 2017, 2:05am UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/8 "2017-02-25T02:05:03Z")
You should pass arrays as `Ref{T}` where `T` is the element type. `Array` should basically never appear in a ccall signature, as it is a Julia object (and no C libraries that I know of expect to be passed Julia arrays).
i.e. try:
```julia
ccall(("sqrinr_","qrupdate-1.1.2/libqrupdate"), Void,
(Ref{Int64}, Ref{Int64}, Ref{Float64}, Ref{Int64}, Ref{Float64}, Ref{Int64}, Ref{Int64}
, Ref{Float64}, Ref{Float64}),
n, q, Q, n+1, R, n+1, n, xp, w)
```
---
### Author:  [@Mattriks](https://discourse.julialang.org/u/Mattriks)
#### Post date: [February 25, 2017, 2:14am UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/9 "2017-02-25T02:14:18Z")
Also here is a simple example:
```fortran
subroutine foo1(n,x,y)
integer*4, intent(in) :: n
integer*4, intent(in), dimension(n) :: x
integer*4, intent(out), dimension(n) :: y
y = 2*x
end subroutine foo1
subroutine foo2(n,x,y)
integer*8, intent(in) :: n
integer*8, intent(in), dimension(n) :: x
integer*8, intent(out), dimension(n) :: y
y = 2*x
end subroutine foo2
```
Compile into a shared library, and then in Julia, e.g.:
```julia
ftest = Libdl.dlopen("ftest.dll")
t = ones(Int32,2)
ccall(Libdl.dlsym(ftest,:foo1_), Void, (Ref{Int32}, Ref{Int32}, Ptr{Int32}), Int32(2), Int32.([3, -1]), t)
println(t)
t = ones(Int64,2)
ccall(Libdl.dlsym(ftest,:foo2_), Void, (Ref{Int64}, Ref{Int64}, Ptr{Int64}), 2, [3, -1], t)
println(t)
Libdl.dlclose(ftest)
```
---
### Author:  [@bdeonovic](https://discourse.julialang.org/u/bdeonovic)
#### Post date: [February 25, 2017, 3:52pm UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/10 "2017-02-25T15:52:54Z")
Thanks guys. It seems to be running, but I’m not getting the results I want. This might be too much to ask but can anyone take a look at my code and find any obvious issues?
The code generates `X` a n by q matrix, `beta=[1,2,3,4,5]`, and generates y ~ N( X\*beta, 1)
Q,R is the QR decomposition of X. I want to use the fortran code to get the updated QR decompositon of X after adding another row (`xp`) to `X`. After I run the fortran code, the matrix Q and R are not correct.
```julia
using Distributions
n=20
p=1
q=5
X = zeros(Float64, n, q)
for i in 1:n
X[i,:] = randn(q)
end
beta = [1,2,3,4,5]
y = rand(MvNormal(X * beta, 1.0))
Q, R = qr(X, thin=false)
## resize Q so that its n+1 by n+1, append zeros to R so its n+1 by q
Qp = vcat(hcat(Q, zeros(n)), zeros(n+1)')
Rp = vcat(R, reshape(zeros( (n-q+1)*q), n-q+1,q))
xp = randn(q)
yp = (xp'*beta)[1]
w = zeros(min(n,q))
ccall(("sqrinr_","libqrupdate"), Void,
(Ref{Int32}, Ref{Int32}, Ref{Float64}, Ref{Int32}, Ref{Float64}, Ref{Int32}, Ref{Int32}, Ref{Float64}, Ref{Float64}),
n, q, Qp, n+1, Rp, n+1, n+1, xp, w)
```
---
### Author:  [@Mattriks](https://discourse.julialang.org/u/Mattriks)
#### Post date: [February 25, 2017, 7:23pm UTC](https://discourse.julialang.org/t/calling-fortran-function/2288/11 "2017-02-25T19:23:59Z")
Here is another example for you to try:
```fortran
subroutine foo3(x,y)
integer*8, intent(in) :: x(:)
integer*8, intent(out) :: y(:)
y = 2*x
end subroutine foo3
```
This example shows that Fortran doesn’t know the size of the Julia array. The subroutine `sqrinr` uses arrays which have unspecified dimensions.