給Ubuntu 18.04安裝軟體時，會遇到類似下面的問題

The following packages have unmet dependencies:
 libvtk7-dev : Depends: libvtk7-java (= 7.1.1+dfsg1-2) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

根據提示，逐步安裝“Depends”後提示的軟體包。最後，Ubuntu 18.04會安裝要求的軟體包，並刪除衝突的軟體包。
下面是根據這個辦法，安裝libvtk7-dev的過程。

$ sudo apt install libvtk7-dev
Reading package lists... Done
......
The following packages have unmet dependencies:
 libvtk7-dev : Depends: libvtk7-java (= 7.1.1+dfsg1-2) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

$ sudo apt install libvtk7-java
Reading package lists... Done
Building dependency tree
Reading state information... Done
... ...
The following packages have unmet dependencies:
 libvtk7-java : Depends: libvtk7-jni (= 7.1.1+dfsg1-2) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

$ sudo apt install libvtk7-jni
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  libqt5x11extras5 libvtk7.1 libvtk7.1-qt
Suggested packages:
  vtk7-doc vtk7-examples
The following packages will be REMOVED:
  libpcl-dev libvtk6-dev libvtk6-java libvtk6-jni libvtk6-qt-dev
The following NEW packages will be installed:
  libqt5x11extras5 libvtk7-jni libvtk7.1 libvtk7.1-qt
0 upgraded, 4 newly installed, 5 to remove and 0 not upgraded.
Need to get 38.6 MB of archives.
After this operation, 127 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
......
Setting up libvtk7-jni (7.1.1+dfsg1-2) ...
Processing triggers for libc-bin (2.27-3ubuntu1.4) ...
 

另外，也可以使用命令“aptitude why-not software-package-name”, 輸出中“Breaks”後的軟體包，就是有衝突的軟體包。解除安裝有衝突的軟體包後，就可以直接安裝需要的軟體包。