# LinearMap : error while running LinearMap
**URL:** https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966
**Category:** General Usage
**Created:** [June 24, 2020, 7:00am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966 "2020-06-24T07:00:05Z")
**Posts on this page:** 18
**Page:** 1
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 7:00am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/1 "2020-06-24T07:00:05Z")
I tried to run Julia-1.6.0 dev version in my laptop. When running the LinearMap function, I encountered an error, which I have attached along with this query. I would like any suggestions to improve.
Thanks in advance,
Sai Krishna
---
### Author:  [@simeonschaub](https://discourse.julialang.org/u/simeonschaub)
#### Post date: [June 24, 2020, 8:00am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/2 "2020-06-24T08:00:13Z")
Please try to avoid posting screenshots and quote your code instead, as this makes it much easier to help you. Also try to make sure, you provide a complete working example, as you didn’t define `multiplyHPsi` anywhere. This thread may be helpful to you:
> [@Please read: make it easier to help you](https://discourse.julialang.org/t/psa-make-it-easier-to-help-you/14757):
>
> Welcome to the Julia Discourse! We are enthusiastic about helping Julia programmers, both beginner and experienced. This public service announcement (PSA) outlines best practices when asking for help. Following these points makes it easier for us to help you and more likely you’ll get a prompt, useful answer. Keywords are highlighted to make it easier to refer to specific points. Choose a descriptive title that captures the key part of your question, eg “plots with multiple axes” instead of …
That said, does your code work on a previous version of Julia? What version of `LinearMaps.jl` are you using? (You can find that out with `]st LinearMaps` in the REPL.)
---
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 9:25am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/3 "2020-06-24T09:25:59Z")
Thank you for your reply. I will quote the entire working example now. The LinearMaps.jl version is 2.6.1.
The code is as follows:
function multiplyHPsi!(nPsi::Vector, Psi::Vector) # requires H2 to have been defined
length(nPsi)==length(Psi) || throw(DimensionMismatch())
dimN = length(Psi) # Dimension of the vector space
N = convert(Int64,log2(dimN)) # Number of spins
dimPsi = tuple(fill(2::Int,1,N)…) # dimsPsi =(2,2,2, …, 2)
a = collect(2:N)
a = [a;1]
cyclperm = tuple(a…) #tuple for cyclic permutation cyclperm = (2, 3, … N, 1)
Psi = reshape(Psi,dimPsi)
nPsi = zeros(dimPsi)
for n=1:N
Psi = reshape(Psi,(4,2^(N-2)))
nPsi = reshape(nPsi,(4,2^(N-2)))
nPsi += H2\*Psi
Psi = reshape(Psi,dimPsi)
nPsi = reshape(nPsi,dimPsi)
Psi = permutedims(Psi,cyclperm)
nPsi = permutedims(nPsi,cyclperm)
end
nPsi = reshape(nPsi,dimN)
return nPsi
end
# Ising model
function buildIsing(h=1.0) # Ising model with transverse magnetic field h (critical h=1 by default)
X = [0 1; 1 0]
Z = [1 0; 0 -1]
I = diagm(0 =\> ones(2))
XX = kron(X,X)
ZI = kron(Z,I)
IZ = kron(I,Z)
H2 = -(XX + h/2\*(ZI+IZ))
return H2
end
# XX model
function buildXX(h=0.0) # XX model with magnetix field h (h=0 by default)
X = [0. 1; 1 0]
Y = [0. -1; 1 0] # we avoid using complex numbers
Z = [1 0; 0 -1]
I = diagm(0 =\> ones(2))
ZI = kron(Z,I)
IZ = kron(I,Z)
H2 = -(kron(X,X)-kron(Y,Y)) + h/2\*(ZI+IZ) # sXsX+sYsY + hZ
return H2
end
display(buildIsing())
display(buildXX())
h = 1
H2 = buildIsing(h) # Hamiltonian
H2 = buildXX()
D,U = eigen(H2)
shiftE = D[end]
H2 = H2 - shiftE\*diagm(0 =\> ones(4)) # remember to re-shift the energy later on!
N = 10 # number of spins
Psi = rand(2^N)
nPsi = rand(2^N)
Psi = Psi/norm(Psi)
init\_steps = 1
energy = ones(0)
initial\_step=1
Nsteps = 0
@time nPsi = multiplyHPsi!(nPsi, Psi) # N = 20 took 4 seconds;
initial\_step += Nsteps
Nsteps = 10
final\_step = initial\_step + Nsteps-1
for n=initial\_step:final\_step
nPsi = multiplyHPsi!(nPsi,Psi)
newenergy = real(Psi’_nPsi)[1] + shiftE_N
energy = [energy; newenergy]
Psi = nPsi/norm(nPsi)
print(n-initial\_step+1, “:”, Nsteps, " ")
end
figure(“Power\_method”,figsize=(14,4))
subplot(121) # Create the 1st axis of a 2x2 arrax of axes
grid(“on”) # Create a grid on the axis
title(“Power method”)
ax = gca()
xlabel(“all iterations”)
ylabel(“Energy”)
plot(energy, marker = “o”)
subplot(122) # Create the 1st axis of a 2x2 arrax of axes
grid(“on”) # Create a grid on the axis
title(“Power method”)
ax = gca()
xlabel(“most recent iterations”)
ylabel(“Energy”)
plot(initial\_step:final\_step, energy[initial\_step:final\_step], marker = “o”)
using LinearMaps; using Arpack
N = 14 # N=14 took 4.5 sec; N=16 took 35 sec; N=18 took 122 sec
m = 1 # how many states?
# this produces a linear map H that can be called from eigs
H = LinearMap{Float64}(multiplyHPsi!, 2^N; isreal = true, ismutating = true) # use this for real symmetric H
#H = LinearMap(multiplyHPsi!, 2^N, isreal=false, ismutating=true, ishermitian=true) # use this for complex hermitian H
@time u, v = eigs(H; nev=m, which=:SR) #:SR stands for smallest real part
Energy = real(u[1] + shiftE\*N) # let us undo the shift in energy
Psi = v
E = Energy
---
### Author:  [@juthohaegeman](https://discourse.julialang.org/u/juthohaegeman)
#### Post date: [June 24, 2020, 9:58am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/4 "2020-06-24T09:58:21Z")
Note that `isreal` is not a keyword argument of `LinearMap`, that’s also the complaint of the `MethodError`. You should specify the `eltype` of your map as you do with `LinearMap{Float64}`. Just leave out the `isreal` will probably resolve your problem.
---
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 10:09am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/5 "2020-06-24T10:09:33Z")
Thank you for the suggestion but I ran into the following error after removing the isreal. And how do you specify the eltype of the map. Please let me know that.
The following is the error:
syntax: invalid keyword argument syntax “true” around In[66]:4
Stacktrace:
[1] top-level scope at none:1
---
### Author:  [@simeonschaub](https://discourse.julialang.org/u/simeonschaub)
#### Post date: [June 24, 2020, 11:19am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/6 "2020-06-24T11:19:17Z")
I am guessing, that you left a semicolon before the positional argument `isreal` instead of a comma. Replacing that with a comma should fix this error. It’s a bit of a confusing error message though, because 1.5 has a new feature, where variables after a semicolon in a function call are interpreted as `x=x`, i.e. a keyword argument where the value is that variable in the current scope. Do you want to open an issue on GitHub, because this should probably throw a more helpful error for `true` and `false`?
---
### Author:  [@juthohaegeman](https://discourse.julialang.org/u/juthohaegeman)
#### Post date: [June 24, 2020, 11:19am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/7 "2020-06-24T11:19:46Z")
I was assuming that you understand a bit the basic concepts in Julia. When I said, leave out the keyword argument `isreal`, this implies also its value:
```julia
H = LinearMap{Float64}(multiplyHPsi!, 2^N; ismutating = true)
```
The `eltype` is what you put in between the curly braces here, `LinearMap{ eltype }`.
In this case, as it seems you want to diagonalize quantum Hamiltonians, it might be useful to specify that this is a symmetric (or hermitian) operator, i.e.
```julia
H = LinearMap{Float64}(multiplyHPsi!, 2^N; ismutating = true, issymmetric = true)
```
---
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 11:44am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/8 "2020-06-24T11:44:05Z")
But once I removed the isreal argument, I got the same error.
---
### Author:  [@juthohaegeman](https://discourse.julialang.org/u/juthohaegeman)
#### Post date: [June 24, 2020, 11:50am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/9 "2020-06-24T11:50:23Z")
Can you post the line which you entered just before the error was thrown, and the error.
---
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 12:07pm UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/10 "2020-06-24T12:07:30Z")
This is the line which I entered before the error :
H = LinearMap{Float64}(multiplyHPsi!; 2^N, true) # use this for real symmetric H
This is the error:
MethodError: no method matching (LinearMaps.FunctionMap{Float64,F1,F2} where F2 where F1)(::typeof(multiplyHPsi!), ::Int64, ::Bool)
Closest candidates are:
(LinearMaps.FunctionMap{T,F1,F2} where F2 where F1)(::Any, ::Int64; kwargs…) where T at /home/sai/.julia/packages/LinearMaps/RjB5x/src/functionmap.jl:20
(LinearMaps.FunctionMap{T,F1,F2} where F2 where F1)(::Any, ::Int64, !Matched::Int64; kwargs…) where T at /home/sai/.julia/packages/LinearMaps/RjB5x/src/functionmap.jl:21
(LinearMaps.FunctionMap{T,F1,F2} where F2 where F1)(::Any, ::Any, !Matched::Int64; kwargs…) where T at /home/sai/.julia/packages/LinearMaps/RjB5x/src/functionmap.jl:22
…
Stacktrace:
[1] LinearMap{Float64}(::Function, ::Int64, ::Vararg{Any,N} where N; kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at /home/sai/.julia/packages/LinearMaps/RjB5x/src/LinearMaps.jl:164
[2] LinearMap{Float64}(::Function, ::Int64, ::Vararg{Any,N} where N) at /home/sai/.julia/packages/LinearMaps/RjB5x/src/LinearMaps.jl:164
[3] top-level scope at In[84]:4
---
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 12:23pm UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/11 "2020-06-24T12:23:46Z")
I am sorry for my mistake about the error. The actual error is:
syntax: invalid keyword argument syntax “true” around In[88]:4
Stacktrace:
[1] top-level scope at none:1
---
### Author:  [@juthohaegeman](https://discourse.julialang.org/u/juthohaegeman)
#### Post date: [June 24, 2020, 1:21pm UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/12 "2020-06-24T13:21:46Z")
Why did you not copy the code I posted?
```julia
H = LinearMap{Float64}(multiplyHPsi!, 2^N; ismutating = true)
```
I think you want to read a bit about basic julia syntax.
---
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 4:44pm UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/13 "2020-06-24T16:44:29Z")
Thanks for your reply. I have used the syntax and read about the LinearMap function. Now, I need to use the eigs function to decompose the resulting matrix. The code is as follows:
N = 14 # N=14 took 4.5 sec; N=16 took 35 sec; N=18 took 122 sec
m = 1 # how many states?
H = LinearMap(multiplyHPsi!, 2^N, ismutating = true, ishermitian = true)
#H = LinearMap(multiplyHPsi!, 2^N, isreal=false, ismutating=true, ishermitian=true) # use this for complex hermitian H
@time u, v = eigs(H; nev=m, which=:SR) #:SR stands for smallest real part
#Energy = real(u[1] + shiftE\*N) # let us undo the shift in energy
#Psi = v
#E = Energy
The error thrown is:
MethodError: no method matching multiplyHPsi!(::SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true}, ::SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true})
Stacktrace:
[1] A\_mul\_B!(::SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true}, ::LinearMaps.FunctionMap{Float64,typeof(multiplyHPsi!),Nothing}, ::SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true}) at /home/sai/.julia/packages/LinearMaps/RjB5x/src/functionmap.jl:112
[2] mul!(::SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true}, ::LinearMaps.FunctionMap{Float64,typeof(multiplyHPsi!),Nothing}, ::SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true}, ::Bool, ::Bool) at /home/sai/.julia/packages/LinearMaps/RjB5x/src/LinearMaps.jl:78
[3] mul! at /home/sai/.julia/packages/LinearMaps/RjB5x/src/LinearMaps.jl:76 [inlined]
[4] (::Arpack.var"#matvecA!#24"{LinearMaps.FunctionMap{Float64,typeof(multiplyHPsi!),Nothing}})(::SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true}, ::SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true}) at /home/sai/.julia/packages/Arpack/o35I5/src/Arpack.jl:156
[5] aupd\_wrapper(::Type{T} where T, ::Arpack.var"#matvecA!#24"{LinearMaps.FunctionMap{Float64,typeof(multiplyHPsi!),Nothing}}, ::Arpack.var"#18#25", ::Arpack.var"#19#26", ::Int64, ::Bool, ::Bool, ::String, ::Int64, ::Int64, ::String, ::Float64, ::Int64, ::Int64, ::Array{Float64,1}) at /home/sai/.julia/packages/Arpack/o35I5/src/libarpack.jl:83
[6] \_eigs(::LinearMaps.FunctionMap{Float64,typeof(multiplyHPsi!),Nothing}, ::UniformScaling{Bool}; nev::Int64, ncv::Int64, which::Symbol, tol::Float64, maxiter::Int64, sigma::Nothing, v0::Array{Float64,1}, ritzvec::Bool) at /home/sai/.julia/packages/Arpack/o35I5/src/Arpack.jl:181
[7] #eigs#16 at /home/sai/.julia/packages/Arpack/o35I5/src/Arpack.jl:66 [inlined]
[8] #eigs#9 at /home/sai/.julia/packages/Arpack/o35I5/src/Arpack.jl:45 [inlined]
[9] macro expansion at ./timing.jl:174 [inlined]
[10] top-level scope at ./In[195]:4
---
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 4:52pm UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/14 "2020-06-24T16:52:50Z")
Sorry my mistake. I forgot write the function to accept AbstractVector instead Vector. This solved the issue.
---
### Author:  [@saikrishna](https://discourse.julialang.org/u/saikrishna)
#### Post date: [June 24, 2020, 4:53pm UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/15 "2020-06-24T16:53:28Z")
Thank you everyone for your valuable time and inputs.
---
### Author:  [@brucelyu](https://discourse.julialang.org/u/brucelyu)
#### Post date: [July 13, 2022, 8:33am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/16 "2022-07-13T08:33:03Z")
Hi! I’m following Vidal’s PSI online course too.
Do you succeed in this notebook?
I found the following strange behavior.
If I define LinearMap like this:
`H = LinearMap{Float64}(multiplyHPsi!, 2^N; ismutating=true, issymmetric = true)`
I need to check whether it does what it should, so I test
```julia
Psi = randn(2^N)
nPsi = randn(2^N)
Psi = Psi / norm(Psi)
nPsi1 = multiplyHPsi!(nPsi, Psi)
nPsi2 = H(Psi)
```
Now, the result `nPsi1` is OK and looks correct; however, `nPsi2` looks like random outcomes and looks nothing close to `nPsi1`, as it should.
I’m confused what goes wrong here.
---
### Author:  [@juthohaegeman](https://discourse.julialang.org/u/juthohaegeman)
#### Post date: [July 15, 2022, 9:31am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/17 "2022-07-15T09:31:11Z")
That’s odd; could you post the full code that gives you the issue, including a working version of `multiplyHPsi!`. You can also put it in a gist and just paste the link here.
---
### Author:  [@brucelyu](https://discourse.julialang.org/u/brucelyu)
#### Post date: [July 20, 2022, 4:12am UTC](https://discourse.julialang.org/t/linearmap-error-while-running-linearmap/41966/18 "2022-07-20T04:12:15Z")
Hi Jutho!
Thank you very much for the reply.
I’ve create and .jl file to reproduce the above-mentioned issue.
Here is the link:
[https://gist.github.com/brucelyu/b038114b507ab5ca241f78a3f93eb0f2](https://gist.github.com/brucelyu/b038114b507ab5ca241f78a3f93eb0f2)