local function dimnarrow(x,sz,pad,dim)

    local xn = x

    for i=1,x:dim() do

        if i > dim then

            xn = xn:narrow(i,pad[i]+1,sz[i])

        end

    end

    return xn

end

local function padzero(x,pad)

    local sz = x:size()

    for i=1,x:dim() do 

      sz[i] = sz[i]+pad[i]*2 

    end

    local xx = x.new(sz):zero()

    local xn = dimnarrow(xx,x:size(),pad,-1)

    xn:copy(x)

    return xx

end

local function padmirror(x,pad)

    local xx = padzero(x,pad)

    local sz  = xx:size()

    for i=1,x:dim() do

        local xxn = dimnarrow(xx,x:size(),pad,i)

        for j=1,pad[i] do

            xxn:select(i,j):copy(xxn:select(i,pad[i]*2-j+1))

            xxn:select(i,sz[i]-j+1):copy(xxn:select(i,sz[i]-pad[i]*2+j))

        end

    end

    return xx

end

function padarray(x,pad,padtype)

-- Example usage:  img = padarray(img,{0, pady, padx},'zero')

    if x:dim() ~= #pad then

        error('number of dimensions of Input should match number of padding sizes')

    end

    if padtype == 'zero' then return padzero(x,pad) end

    if padtype == 'mirror' then return padmirror(x,pad) end

    error('unknown paddtype ' .. padtype)

end